Hypertrophy

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Hypertrophy is an increase in muscular size. Research comparing the effects of training programs over time can help identify which features are important for maximizing hypertrophy and which features make no difference. 

In untrained individuals, heavy relative loads (<15RM) might be superior to a light relative loads (>15RM) for hypertrophy but the research is slightly unclear. In trained individuals, heavy and light relative loads produce similar increases in muscular size.

For untrained individuals, several studies show that multiple sets leading to greater total volume appear to cause greater hypertrophy. For trained individuals, there is much less evidence but multiple sets leading greater total volume may be superior to single sets.

For untrained individuals, training closer to muscular failure appears to lead to greater hypertrophy. For trained individuals, training closer to muscular failure may also lead to greater hypertrophy.

For untrained individuals, altering volume-matched training frequency does not seem to have any effect on hypertrophy. For trained individuals, a higher volume-matched training frequency might to be superior to a lower volume-matched frequency for hypertrophy.

For untrained individuals, rest period duration seems to make little difference to hypertrophy. For trained individuals, longer rests may be better, as they allow the accumulation of greater volume loads.

For untrained individuals, a larger ROM appears to lead to greater hypertrophy than a shorter ROM. For trained individuals, there is unfortunately currently no evidence available.

For untrained individuals, deliberately slowing down bar speed to increase time under tension seems to make little difference to hypertrophy. For trained individuals, slowing down the eccentric phase seems to lead to greater hypertrophy.

For trained individuals using variable-load external resistance, there is limited evidence that eccentric muscle actions might be superior to concentric muscle actions. For untrained individuals using variable-load external resistance, there is conflicting evidence that eccentric muscle actions might be superior to concentric muscle actions.

For trained individuals using constant-load external resistance, there is limited evidence that eccentric muscle actions might be superior to concentric muscle actions. For untrained individuals using constant-load external resistance, there does not seem to be any difference between eccentric and concentric muscle actions.

For trained individuals, periodization makes little difference for hypertrophy. There is limited evidence to suggest that reverse linear is worse than linear but linear and non-linear approaches appear to have equal merit. For untrained individuals, there are conflicting indications that periodization might be superior to non-periodization and that non-linear might be superior to linear.

For trained individuals, using pre-exhaustion techniques is unlikely to cause larger improvements in muscular size than conventional resistance training. The effects of drop sets, supersets and forced repetitions are unclear. However, the rest pause technique may be beneficial, possibly because it permits greater volume load to be used.

Adding single-joint exercises to an existing program of multi-joint exercises does not appear to enhance gains in muscular size (but might affect where gains occur). Using several multi-joint exercises appears to cause more consistent hypertrophy within a muscle group than using one multi-joint exercise.

Genetics appear to play an important role in differentiating between individuals who display very marked hypertrophy (responders) and those who do not (non-responders). However, we are currently unable to identify those genes or groups of genes that are associated with responsive or non-responsive tendencies.



CONTENTS

Full table of contents

  1. Background
  2. Relative load (percentage of 1RM)
  3. Volume
  4. Muscular failure
  5. Frequency (whole body or split)
  6. Rest period duration
  7. Range of motion
  8. Bar speed (time under tension)
  9. Muscle action (variable)
  10. Muscle action (constant load)
  11. Periodization type
  12. Exercise selection
  13. Advanced techniques
  14. Genetics and hypertrophy
  15. References
  16. Contributors
  17. Provide feedback


BACKGROUND

PURPOSE

This section provides the background to hypertrophy, including the various different measurement methods. 

KEY INFORMATION

Introduction

Hypertrophy is an increase in muscle size. It is thought to arise because of a sustained excess of muscle protein synthesis (MPS) over-and-above muscle protein breakdown (MPD) over a period of time, leading to net protein accretion.

Measuring muscle size

Hypertrophy is most commonly measured by muscle cross-sectional area (CSA), muscle volume, limb girth, or lean body mass. Measures of muscle CSA or volume are the most common in studies directly exploring increases in the muscle size of specific muscles as a result of different strength training programs. Measures of lean body mass are more often used only where whole body muscle mass is of interest, such as when testing the effects of different protein supplements. Muscle CSA can be measured either perpendicular to the longitudinal axis of the muscle, which is called anatomical CSA, or perpendicular to the longitudinal axis of the muscle fibers, which is called physiological CSA. Anatomical CSA is easier to measure, as it only requires a single scan. Physiological CSA is harder to identify, as it requires measurement of the pennation angle of the muscle as well.

Measurement methods for muscle size

Changes in muscle CSA or volume are most commonly measured using magnetic resonance imaging (MRI) scans, computed tomography (CT) scans or ultrasonography. Muscle volume is calculated by measuring multiple different slices along the length of the muscle, and then adding them together in blocks. Girth is measured using a tape measure and is rarely now used in comparison with more sophisticated methods. Changes in lean body mass (strictly fat-free mass) are most commonly measured using dual-energy X-ray absorptiometry (DEXA) scans or Bod Pod analysis. The exact measurement method used for hypertrophy may be important, as different methods have been found to produce different results when comparing training variables (Weiss et al. 2000).

Requirement for hypertrophy

Hypertrophy is often desirable for several reasons: (1) aesthetic, (2) sporting, and (3) functional purposes. While most people associate the deliberate acquisition of additional muscle mass with bodybuilders, hypertrophy is also very important for athletes participating in strength sports as it contributes to performance. For example, Brechue et al. (2002) found that both fat-free mass and muscular CSA at individual sites were very good predictors of powerlifting ability.

Hypertrophy is also important for elderly people, as low levels of muscle mass are strongly correlated with a loss of functional independence and mobility and an increased risk of disability and functional impairment (Janssen et al. 2002; Janssen et al. 2004; Visser et al. 2005; Delmonico et al. 2007).

Relationship between muscle size and strength

The relationship between muscle size and strength is complex, and there are many different opinions among experts. Strength can be affected by two different groups of factors (also called determinants): peripheral and central. Peripheral factors are those inside the muscle itself, while central factors are those inside the central nervous system (CNS). Peripheral factors include:

  • Muscle size
  • Moment arm length
  • Length of the fascicles
  • Prevailing pennation angle of the fibers
  • Muscle fiber type
  • Single fiber contractile properties

Muscle force can also be affected by central factors, which include:

  • Coordination for the movement or exercise
  • Size of the neural drive to the prime mover muscle
  • Size of the neural drive to the stabilizer muscles
  • Size of the neural drive to the synergist muscles
  • Size of the antagonist coactivation levels

To identify the relationship between these factors and muscular strength, researchers often use controlled studies, in which they measure single-joint isometric and slow speed, isokinetic concentric force production. They do this to reduce the impact of the factors that make strength specific, which have a huge influence during not perfectly stable, multi-joint, high-velocity, or eccentric exercises. Such studies fall into two categories:

  1. Comparisons between individuals cross-sectionally, and
  2. Comparisons within individuals, as a result of strength training.

The first category tells us what makes some people stronger than others. The second category tells us what makes one person stronger after training. Importantly, the factors are not always the same. For example, one very recent and high-quality study performed a cross-sectional analysis and showed that muscle size was a very strong predictor (r = 0.68 – 0.76) of muscle strength (Trezise et al. 2016).

Muscle force can be affected by many properties of a muscle (not just its size), including muscle size, moment arm length, the length of the fascicles, the prevailing pennation angle of the fibers, the muscle fiber type, and even the single fiber contractile properties (which can differ even when muscle fiber types are similar). Muscle force can also be affected by the coordination that we have for the movement or exercise, the size of the neural drive to the prime mover muscle, to the stabilizer muscles, and by the size of the antagonist coactivation levels. To identify the relationship between these factors and muscular strength, researchers often use controlled studies, in which they measure single-joint isometric and slow speed, isokinetic concentric force production. They do this to reduce the impact of the factors that make strength specific, which have a huge influence during not perfectly stable, multi-joint, high-velocity, or eccentric exercises. Such studies fall into two categories: (1) those that compare individuals cross-sectionally between each other, and (2) those that compare the changes as a result of strength training. The first category tells us what makes some people stronger than others. The second category tells us what makes one person stronger after training. The factors are not always the same! In this study, the researchers measured knee extension torque in a cross-sectional study, and assessed factors that might influence strength in that movement. Using correlations, they identified which of the factors might be most closely related to strength. In this very comprehensive and careful assessment, muscle size was still found to be a large predictor of strength, but there were also a great many other moderate predictors, including those inside the muscle (pennation angle, fascicle length, and moment arm length) and in the central nervous system (as indicated by voluntary activation and EMG). This shows that muscle size is not the only determinant of strength (although it is the largest).

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In contrast, long-term studies exploring the relationship between gains in strength and hypertrophy (rather than strength and muscle size) tend to report weaker associations. For example, Erskine et al. (2010) showed that the relationship between strength and hypertrophy was moderate (r = 0.48), while the relationship between strength and specific tension (a compound measurement of the single fiber contractile properties) was far stronger (r = 0.79).

Muscle force can be affected by many factors. We generally divide the factors into two types: (1) peripheral (those inside the muscle) and (2) central (those in the central nervous system). Peripheral factors include muscle size, moment arm length, the length of the fascicles, the prevailing pennation angle of the fibers, the muscle fiber type, and even the single fiber contractile properties. Central factors include the level of coordination that we have for the exercise, the size of the neural drive to the prime mover muscle, to the stabilizer muscles, and by the size of the antagonist coactivation levels. To assess the impact of each of these factors, researchers can use either comparisons between individuals, or comparisons from before to after a training program. Obviously, assessing the importance of the factors as a result of a training program is more insightful. In this study, the researchers assessed the importance of many factors over a long-term training program. Hypertrophy was only moderately associated with increases in strength. In contrast, changes in specific tension were strongly associated. Specific tension is a measurement of the force per unit cross-sectional area, corrected for pennation angle. The force is taken from the involuntary force during electrically-stimulated contractions, and therefore does not include possible alterations in neural drive. The main factors believed to influence specific tension are alterations in the muscle fiber type, increases in myofibrillar packing density, or changes in the structure of the individual muscle fiber and its ultrastructure, which could increase lateral force transmission.

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Training methods for hypertrophy

A great deal of research has been performed exploring the role of resistance training for hypertrophy (Tan, 1999; Hunter et al. 2004; Wernbom et al. 2007; Adams & Bamman, 2012). However, there are also indications that aerobic exercise can produce a degree of hypertrophy in some muscle groups and in some populations (Ozaki et al. 2013; Konopka & Harber, 2014). Additionally, a relatively novel method of training called Blood Flow Restriction (BFR) training has been the subject of considerable research in recent years (Pope et al. 2013; Pearson & Hussain, 2014). This technique can be used with either resistance training or with aerobic exercise methods to produce hypertrophy (Abe et al. 2012; Ozaki et al. 2013).

Guidance for hypertrophy

INTRODUCTION

When identifying the best methods for developing most qualities in strength and conditioning (including strength, power, rate of force development, and muscular size), a review of the research quickly reveals a huge range of articles, of differing types. Many of these articles present completely different viewpoints, and often provide contradictory recommendations. Therefore, it is necessary to have a system to grade which types of information are more reliable than others. The generally accepted order is meta-analyses and systematic reviews of methods at the top, and expert opinion at the bottom.

LEVELS OF EVIDENCE

Guidance for hypertrophy ranges from advice from expert strength coaches who provide advice based on their personal observations (level 4 evidence) through to research-based position stands (levels 1 – 3 evidence) produced by leading institutions, such as the American College of Sports Medicine (Kraemer et al. 2002; ACSM, 2009). The best evidence is taken from research, as this controls for several confounding effects that are not controlled for in personal observations, such as survivorship bias. Such research includes both long-term trials (which measure hypertrophy directly) and short-term trials (which measure markers of muscle growth, indirectly). The best evidence comes from long-term trials, particularly those that compare the effects of two or more different training program variables on the resulting hypertrophy. Many of the formal position stands have been criticized (Carpinelli, 2004; Carpinelli, 2009) on the basis that they fail to cite enough evidence from long-term trials to support each recommendation made regarding individual program variables. The most fierce criticism for the ACSM position stand in 2002 came from a researcher who appears to have originally been a member of the review group for the position stand (Carpinelli, 2004; Fisher & Steele, 2012). Unsurprisingly, some recent attempts have been made to better guidance, by using solely the long-term trials by individual groups of researchers (Fisher et al. 2011; Fisher et al. 2013) and these provide a different perspective, although the extent to which they provide an equal balance of all of the available research is unclear.

Variability of the training response

INTRODUCTION

Strength training tends to produce a very wide set of responses in groups of subjects taking part in the same training program (Hubal et al. 2005; Ahtiainen et al. 2016). Hubal et al. (2005) carried out a study in 585 subjects (342 females and 243 males) who performed 12 weeks of 1-arm biceps curl strength training. The changes in biceps brachii size ranged from -2 to +59% (-0.4 to +13.6cm) and 1RM biceps curl strength gains ranged even more widely from 0 to +250% (0 to +10.2kg). Some of this variability is thought to arise from differences in baseline training status, some is thought to arise from genetic qualities, and some is thought to arise from the behaviours that the subjects display during the training period (e.g. eating habits, effort, etc.).

EFFECT OF GENETICS

Although it is well-known that there is a relationship between sports performance and genetics, the precise impact of genetics on hypertrophy is hard to quantify. Even so, it doubtless contributes to the variability of the training response. In their large-scale investigation Hubal et al. (2005) were unable to identify any specific Single Nucleotide Polymorphisms (SNPs) that could predict superior hypertrophy compared to others. However, there are many ways in which genotypes could affect gains in muscle size after strength training. For example, genetic susceptibility to muscle damage during strength training could easily lead to some individuals requiring more time to recover than others (Baumert et al. 2016), and there is evidence that satellite cell characteristics may influence the hypertrophic response (Bamman et al. 2007; Petrella et al. 2008). Moreover, a long-term training study recently confirmed that there is clearly a genetic component relating to repetition ranges, as Jones et al. (2016) reported that matching genotypes based on a selection of SNPs known to influence either endurance or power-based test performances was able to predict the type of training that was most effective. This may therefore imply that some of the variability observed in groups of subjects after a strength training program arises because their repetition ranges are not matched to their genotypes.

SECTION CONCLUSIONS

To reduce the risk of error, analysis of the optimal methods for hypertrophy should be based around a review of well-controlled long-term trials comparing individual resistance training variables.


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RELATIVE LOAD (PERCENTAGE OF 1RM)

PURPOSE

This section explores whether training with a conventionally heavy load of <15RM is more effective than training with a much lighter load of >15RM for hypertrophy. This is achieved by looking at long-term studies that compare different programs of training with heavy and light relative loads for increasing muscular mass or size.

DEFINITIONS

Resistance training exercises can be performed with any load. The weight lifted may range from a load that can be lifted only once to loads that can be lifted a great many times. Since the absolute load (in kg or lbs) that an individual can lift varies greatly from one person to the next, it is conventional in resistance training programs to use percentages of one repetition maximum (1RM) when specifying the loads to be used. Percentage of 1RM is sometimes referred to as “intensity”. However, as various reviewers have observed [Fisher and Smith (2012), Steele (2013), Fisher and Steele (2014), and Schoenfeld (2014)], this term is ambiguous as it could be taken to imply a reference to effort that is not intended. Effort may not be the same as percentage of 1RM, particularly where inter-individual differences exist in respect of the number of repetitions that can be performed at a given load. For the sake of clarity, alternative suggestions have been made regarding terminology, including “intensity of load” and “relative load”. The exact definitions of heavy, moderate and light relative loads differ substantially between research articles. In the study of hypertrophy, it is very common to see a dichotomy between “heavy” and “light” loads, where “heavy” comprises both heavy and moderate loads. In such cases, the dividing line between heavy and light is defined variously by reviewers as >50% of 1RM (Schoenfeld, 2013), >60% of 1RM (Schoenfeld, 2013), >65% (McDonagh and Davies, 1984; Schoenfeld, 2010) or >70% (Spiering et al. 2008; ACSM, 2009).

PROBLEMS

Force-velocity relationship

Where maximal bar speeds are used, the force-velocity relationship is a confounding factor when comparing groups training with different relative loads. This is because the group training with the heavier relative load must use a slower bar speed and consequently performs each repetition with a longer repetition duration and (depending on whether volume is measured as sets x repetitions or sets x repetitions x relative load) potentially also a longer total time under tension for the workout. However, when comparing two groups training with different relative loads in which sub-maximal bar speeds are used, the force-velocity relationship does not cause a problem. This is because the same bar speed can be used in both cases (or a different bar speed in order to maintain total time under tension across the workout by manipulating repetition duration).

Volume

Volume can be a confounding factor during long-term hypertrophy training programs for at least two reasons.

Firstly, volume can be very individual, as some individuals perform very different numbers of repetitions with the same percentage of 1RM. Thus, where different training groups are being compared that are performing programs using different relative loads, some individuals might perform a greater volume of work than others. While it is noted that several investigations have reported some variation in respect of the number of repetitions that can be performed with a given percentage of 1RM (Hoeger, 1987; Hoeger, 1990; Shimano, 2006; and Moraes, 2014), there does appear to be some degree of reliability in the extent to which prediction equations can be used (Desgorces, 2010). Moreover, the effect of exercise selection seems to be far more important for predicting the number of repetitions that can be performed with a given percentage of 1RM than the exact nature of the population (Hoeger, 1987; Hoeger, 1990; Shimano, 2006; Moraes, 2014; and Desgorces, 2010).

Secondly, both volume and increases in volume can be greatly affected by the choice of relative load. Schoenfeld et al. (2016) found that volume load is much greater when using light loads compared to heavy loads, and also that the increases in volume load tend to be greater after a long-term training program. This is probably because of the superior increases in muscular endurance that occur with light loads, in accordance with other muscular adaptations along the strength-endurance continuum.

META-ANALYSES

Meta-analyses indicate that a higher relative load could be superior to a lighter relative load for optimising gains in muscle mass but there is uncertainty on account of a lack of statistical significance. Schoenfeld (2014b) recently performed a meta-analysis in trained and untrained subjects to compare the effects of high (>65% of 1RM) and low (<60% of 1RM) relative loads during resistance training programs on gains in muscle size. It was found that there was a non-significant trend for the pooled effect size for hypertrophy to be greater with high than with low relative loads loads (effect sizes: 0.82 ± 0.17 vs. 0.39 ± 0.17).

MECHANISMS OF HYPERTROPHY IN RELATION TO RELATIVE LOAD

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Mechanical loading

The most common stimulus for hypertrophy is the application of mechanical loading. There are two ways in which a greater relative load might be expected to lead to a greater mechanical loading effect than a lighter relative load and thereby create a larger hypertrophic stimulus. Firstly, a greater relative load is heavier. Secondly, according to the force-velocity relationship, when greater absolute moment is generated at a joint, the angular velocity of that joint must be lower (so long as maximal bar speeds are used). As a result of this relationship, higher relative loads require slower bar speeds and longer repetition durations. Therefore, a higher relative load might be expected to lead to the activation of a number of motor units for a longer period of time. It is generally assumed that the hypertrophic response to the magnitude of the mechanical loading (as expressed by relative load) is non-linear insofar as there appears to be a definite threshold below which no hypertrophy can occur (see review by Schoenfeld, 2013) and a threshold above which little or no further hypertrophy occurs in response to increasing relative load. The existence of a threshold of relative load below which no meaningful stimulus for hypertrophy will occur has been assumed largely upon the empirical observation that people generally do not experience hypertrophy from carrying out activities of daily living unless such tasks represent a significant challenge to them, as they can do for frail, elderly populations. However, it has also been the subject of extensive review (Schoenfeld, 2013).

Metabolic stress

A secondary stimulus for hypertrophy is thought to be exercise-induced metabolic stress (Schoenfeld, 2010; Schoenfeld, 2013). There is a clear mechanism by which greater numbers of repetitions, as are typically performed during sets with low-to-moderate relative loads could lead to greater metabolic stress and acute cellular hydration than sets performed with high relative loads, as muscular contractions above a certain threshold of maximum voluntary isometric contraction force prevent venous return. Since metabolic stress arises primarily from the prevention of venous return and the consequent buildup of metabolites within the muscle, longer-duration sets with low-to-moderate relative loads would be expected to lead to greater metabolic stress and consequently greater hypertrophy, so long as all other factors remained constant. The relative load at which muscular contractions prevent venous return or even occlude blood flow completely is of great interest in the context of metabolic stress. The effect of relative load on occlusion seems to vary between muscles (Bonde-Petersen et al. 1975; Sadamoto et al. 1983) and between individuals of different strength levels (Barnes 1980), with stronger individuals achieving occlusion at much lower relative loads. Some researchers have assumed that 40% of MVC is sufficient to restrict muscle blood flow (Tanimoto et al. 2008) while 50% of 1RM is often presented as a rule of thumb for a threshold above which muscular contractions in the prime movers are strong enough to stop circulation (Allen et al. 2008). Thus, >50% of 1RM is of particular interest for researchers and is often used to compare heavy and light loads.

Summary

In summary, a higher relative load might be effective than a low relative load for hypertrophy on the basis that the tensile force in the muscle is larger in magnitude and may last for a longer period of time, assuming bar speeds are maximal. Whether this relative load needs to be greater only than a certain threshold or whether there is a dose-response effect is unclear. However, a moderate relative load might be more effective than a high relative load where volume is matched because it permits increased metabolic stress.

EFFECT OF RELATIVE LOAD ON MOLECULAR SIGNALING FOR HYPERTROPHY

Selection criteria

Population – any subjects

Intervention – single resistance training workouts, where >2 workouts involved training with different relative loads

Comparator – the other workout

Outcome – measures of molecular signaling associated with hypertrophy

Results

The following studies were identified: Martineau (2001), Eliasson (2006), Lamon (2009), Wilborn (2009), Kumar (2009), Burd (2010a), Holm (2010), Taylor (2012), Agergaard (2013), Gehlert (2014), Popov (2014).

Findings

There are conflicting results from studies comparing the molecular signalling responses between heavy and light relative loads. Some studies indicate that molecular signalling responses are greater with heavier loads but other studies show no effect.

EFFECT OF RELATIVE LOAD ON MUSCLE PROTEIN SYNTHESIS

Selection criteria

Population – any subjects

Intervention – single resistance training workouts, where >2 workouts involved training with different relative loads

Comparator – the other workout

Outcome – measures of muscle protein synthesis

Results

The following studies were identified: Kumar (2009), Holm (2010).

Findings

There are some indications that heavier relative loads may lead to greater muscle protein synthesis than lighter relative loads (Holm et al. 2010) but not all studies report this effect (Kumar et al. 2009).

EFFECT OF RELATIVE LOAD ON HYPERTROPHY (UNTRAINED)

Selection criteria

Population – untrained subjects

Intervention – resistance-training, where >2 groups trained with different relative loads and at >1 group used light loads (as defined as <50% of 1RM) and at >1 group used heavy loads (defined as >50% of 1RM)

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Weiss (2000), Campos (2002), Tanimoto (2006), Leger (2006), Popov (2006), Holm (2008), Tanimoto (2008), Lamon (2009), Schuenke (2012), Mitchell (2012), Ogasawara (2013), Van Roie (2013), Reid (2014), Morton (2015), Fink (2016).

Findings

Of these studies, 4 reported that heavy loads were superior, while the remainder mainly found no differences between groups. Heavy loads might only be somewhat beneficial for hypertrophy in this population.

EFFECT OF RELATIVE LOAD ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >2 groups trained with different relative loads and at >1 group used light loads (as defined as <50% of 1RM) and at >1 group used heavy loads (defined as >50% of 1RM)

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Schoenfeld (2015b).

Findings

The single study reported that the heavy (8 – 12RM) and light (25 – 35RM) load groups produced similar increases in the muscle thickness of the elbow flexors (5.3 vs. 8.6%), elbow extensors (6.0 vs. 5.2%), and quadriceps (9.3 vs. 9.5%). This suggests that heavy and light load training produces similar increases in muscular size in trained populations.

EFFECT OF VARIED VS. CONSTANT LOADS ON HYPERTROPHY

Selection criteria

Population – any subjects

Intervention – resistance-training, where >2 groups trained and where >1 group trained using constant loads and >1 group trained using a range or varying loads

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Fonseca (2014), Fink (2016).

Findings

These studies found minimal differences between the groups training with varied loads and the groups training with constant loads. This may indicate that there is no specific benefit from varying repetition ranges over the course of a training program, except for the purpose of maintaining interest and motivation.

SECTION CONCLUSIONS

In untrained individuals, heavy relative loads (<15RM) might be superior to a light relative loads (>15RM) for hypertrophy but the research is slightly unclear. In trained individuals, heavy and light loads produce similar increases in muscular size.


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VOLUME

PURPOSE

This section explores whether training with a higher volume is more effective than training with a lower volume for hypertrophy. This is achieved by looking at long-term studies that compare different volumes of training for increasing muscular mass or size.

DEFINITIONS

For the purposes of analyzing volume as a training variable in its own right, volume can be very simply defined as the number of sets of an exercise. Thus, in the vast majority of studies investigating the effect of training volume on hypertrophy multiple sets of an exercise are compared with single sets. In a small minority, a larger number of sets of a fixed number of repetitions are compared with a smaller number of sets of the same number of repetitions. For controlling volume when analyzing the effects of other training variables (such as relative load, proximity to muscular failure, range of motion, rest period duration, bar speed, muscle action, or periodization type), at least three methods of equating volume between conditions are possible. Firstly and most easily, volume can be defined as the number of sets x the number of repetitions. However, this is problematic when comparing the effects of training variables that involve different absolute or relative loads, as either the total amount of weight lifted differs or the proximity to muscular failure differs or both. Consequently, other methods of equating volume have been developed. One method involves equating the mechanical work performed by reference to the load lifted (number of sets x the number of repetitions x the absolute load). This has been termed the “volume load” (Stone et al. 1998). However, where different muscle actions, sub-maximal bar speeds, or relative loads are compared this will likely lead to differences in proximity to muscular failure between conditions.

PROBLEMS

When studying the effect of any individual training variable on hypertrophy, a major problem is the extent to which other training variables can be fixed between the two groups being compared. The most important training variables to fix are those that have been found to have the biggest effect on hypertrophy. In the case of volume, there are few other training variables that have been found to have as significant an effect. However, since volume can be increased by simply adding extra sets onto a workout, it is relatively easy to control for other potential confounding factors, such as proximity to muscular failure, frequency, and relative load.

META-ANALYSES

Few meta-analyses have been performed to assess the effects of volume on hypertrophy. Krieger (2010) observed that multiple sets are associated with 40% greater hypertrophy-related effect sizes than single sets, in both trained and untrained subjects. There are two significant challenges associated with studying the effect of any training variable on hypertrophy that are useful to consider before interpreting the findings of a meta-analysis. In respect of the meta-analysis performed by Krieger (2010), the main challenges have been outlined in an extensive analysis by Fisher (2012). The main issues raised in this commentary are set out below. Firstly, it is problematic that the magnitude of hypertrophy following a resistance training program is generally much smaller than the gains in strength. Since effect sizes are usually calculated as the mean divided by the standard deviation, the small magnitude of the mean increase means that the effect sizes that are reported following a resistance training intervention tend to be quite small. When comparing one resistance training intervention comprising a high volume with another comprising a lower volume, the effect sizes are even smaller. Thus, when considering a meta-analysis of effect sizes to assess the overall effect of a training variable on hypertrophy, it is likely that many of the individual studies will report no overall significant effect while the meta-analysis could report an overall effect because of the type II error occurring within each study. Secondly, a related issue is that many studies exploring the effects of different resistance training programs tend to display a great deal of variability between subjects (e.g. Hubal et al. 2005; Bamman et al. 2007; review by Timmons, 2011). This large variability increases the magnitude of the standard deviation considerably. Since effect sizes are usually calculated as the mean divided by the standard deviation, this further reduces the effect sizes that are reported following a resistance training intervention. Thus, when considering a meta-analysis of effect sizes to assess the overall effect of a training variable on hypertrophy, it is likely that many of the individual studies will report no overall significant effect while the meta-analysis could report an overall effect because of the type II error occurring within each study. To counter these two issues, it is important to use studies that are designed to bring about large increases in muscle mass with comparatively low inter-individual variability or at least sufficient statistical power to counter the effects of such variability. The main tools that researchers have to achieve this are long study durations and large sample sizes. Unfortunately, owing to funding constraints, most trials studying hypertrophy tend to involve relatively few subjects over short durations. Other methods for reducing the inter-individual variability that researchers have only recently begun to investigate include the use of a pre-intervention intervention, in which responders and non-responders are identified. However, this method of identifying and reducing inter-individual variability has not yet been implemented in the comparison of training variables.

MECHANISMS OF HYPERTROPHY IN RELATION TO VOLUME

[Read more: mechanisms of hypertrophy]

Mechanical loading

The main stimulus for hypertrophy is thought to be the application of mechanical loading. Greater stimulus is thought to arise from more prolonged periods in which the muscle is subjected to this mechanical load. Hence, a greater volume of training might be assumed to be more effective than a smaller volume of training, as it involves a longer duration of time during which the muscle is exposed to the stimulus. Nevertheless, it is almost certain that no linear relationship between volume and hypertrophic stimulus exists but rather than a plateau occurs after a certain point has been reached, within the boundaries of a certain time course. This can be deduced from a number of animal trials that have exposed rodent subjects to excessive training volume with insufficient recovery and found that this leads to muscular atrophy (Souza et al. 2011; Souza et al. 2014). On this basis, it is assumed that there is a specific training volume over a specific certain period of time that leads to maximum hypertrophy and increasing the volume further will not lead to bigger increases in muscular size and may in fact lead to decreases in muscular size if the volume becomes excessive.

Summary

In summary, a higher volume might be effective than a lower volume for hypertrophy on the basis that the tensile force in the muscle is longer in duration, subject to adequate recovery being possible. Whether this volume needs to be greater only than a certain threshold or whether there is a dose-response effect is unclear.

EFFECT OF VOLUME ON MOLECULAR SIGNALING FOR HYPERTROPHY

Selection criteria

Population – any subjects

Intervention – single resistance training workouts, where >2 workouts involved training with different volumes

Comparator – the other workout

Outcome – measures of molecular signaling associated with hypertrophy

Results

The following studies were identified: Wilborn (2009), Terzis (2010), Burd (2010), Taylor (2012), Hulmi (2012), Kumar (2012).

Findings

There are some indications that a greater training volume appears to lead to greater molecular signalling responses than a smaller training volume. However, not all studies have reported these effects.

EFFECT OF VOLUME ON MUSCLE PROTEIN SYNTHESIS

Selection criteria

Population – any subjects

Intervention – single resistance training workouts, where >2 workouts involved training with different volumes

Comparator – the other workout

Outcome – measures of muscle protein synthesis

Results

The following studies were identified: Burd (2010).

Findings

There are some indications that a greater training volume appears to lead to a greater acute muscle protein synthesis than a smaller training volume. However, the literature is currently very limited.

EFFECT OF VOLUME ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >2 groups trained with different volumes (usually by performing different numbers of sets of the same exercise)

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Ostrowski (1997), Rhea (2002).

Findings

Of these studies, both reported no differences between groups. Higher volumes might therefore be similar in effect to lower volumes for hypertrophy in this population, although given the picture presented by the studies in untrained subjects and the findings of meta-analyses, this is likely a function of the small body of literature.

EFFECT OF VOLUME ON HYPERTROPHY (UNTRAINED)

Selection criteria

Population – untrained subjects

Intervention – resistance-training, where >2 groups trained with different volumes (usually by performing different numbers of sets of the same exercise)

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Galvão (2005), Marzolini (2008), McBride (2003), Munn (2005), Rønnestad (2007), Starkey (1996), Bottaro (2011), Sooneste (2013), Radaelli (2013), Radaelli (2013a), Correa (2014), Radaelli (2014), Radaelli (2014a), Radaelli (2014b).

Findings

Of these studies, 6 reported a superior effect of higher volumes while the remainder reported no differences between groups. Higher volumes are therefore likely to be superior to lower volumes for hypertrophy in this population. There is also some evidence for a dose-response, as shown by Radaelli et al. (2013a).

SECTION CONCLUSIONS

For untrained individuals, several studies show that multiple sets leading to greater total volume appear to cause greater hypertrophy. For trained individuals, there is much less evidence but multiple sets leading greater total volume may be superior to single sets.


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MUSCULAR FAILURE

PURPOSE

This section explores whether training to muscular failure, or with closer proximity to fatigue, is superior for hypertrophy. This is achieved by looking at long-term studies that compare whether a program where subjects train to muscular failure is better than a program where subjects do not train to muscular failure for increasing muscular mass or size.

DEFINITIONS

Muscular failure is a term frequently used in research studies investigating resistance training programs but precise definitions of this term are infrequently discussed. Willardson (2007) defined muscular failure as “the point during a resistance exercise set when the muscles can no longer produce sufficient force to control a given load”. Schoenfeld (2010) tightened this definition by stating that muscular failure involved “the point during a set when muscles can no longer produce necessary force to concentrically lift a given load.” This definition therefore necessitates the use of concentric muscle actions. In their review, Fisher et al. (2011) tightened the definition even further by defining muscular failure as “the inability to perform any more concentric contractions, without significant change to posture or repetition duration, against a given resistance.” Whether such additions are necessary to the original definition provided by Willardson (2007) is probably a moot point. The important factor of the definition is that muscular failure can only be defined in relation to a given load. This should be immediately apparent when bodybuilders are observed performing repetitions to failure and then immediately dropping the weight and using a lighter weight to continue performing several more repetitions. Thus, muscular failure does not mean that a muscle is incapable of performing further muscle actions and therefore we cannot say that muscular failure is equivalent to being maximally fatigued (Willardson, 2007). Muscular failure means that a muscle is incapable of expressing force at the same level as it was able to previously, such that it is no longer able to move an arbitrary weight that was set for the task at hand.

PROBLEMS

When studying the effect of any individual training variable on hypertrophy, a major problem is the extent to which other training variables can be fixed between the two groups being compared. The most important training variables to fix are those that have been found to have the biggest effect on hypertrophy (i.e. volume). In the case of muscular failure, it is relatively easy to control for the effect of volume while varying whether individuals train to muscular failure by simply inserting an intra-set rest period. Also, in the research literature exploring the effect of muscular failure on hypertrophy, it is most common for the effect of muscular failure to be assessed by comparing two groups, one that uses an intra-set rest period and that does not. However, in practice, this is not how individuals who do not train to muscular failure actually perform resistance-training. Such individuals generally stop slightly short of muscular failure, leaving a repetition or two in the tank. Given the observations made above, this could be important. There is therefore a discrepancy between the research literature and general practice, indicating a lack of ecological validity.

MECHANISMS FOR HYPERTROPHY IN RELATION TO MUSCULAR FAILURE

[Read more: mechanisms of hypertrophy]

Mechanical loading

[Read more: EMG]

The main stimulus for hypertrophy is thought to be the application of mechanical loading. Mechanical loading can be applied both actively (through neural activity leading to motor unit recruitment and contractile activity) or passively (through passive stretch). Active muscle actions involve a neural signal that activates motor units in the muscle, which each recruit a group of dedicated muscle fibers. Henneman’s size principle (see reviews by Enoka, 1984; Heckman and Enoka, 2012; Bawa et al. 2014) states that smaller and weaker motor units (innervating few muscle fibers) are recruited before larger and stronger motor units (innervating larger numbers of muscle fibers). Thus, muscular recruitment proceeds progressively from small to large motor units with increasing magnitude of the neural signal. It is thought that the recruitment of the motor units is necessary for the subsequent hypertrophy of the associated muscle fibers. However, it is debated whether muscular failure produces full motor unit recruitment (Stone et al. 1996; Burd et al. 2012a; Van Roie et al. 2013; Burd et al. 2013; Schuenke et al. 2013; Akima & Saito, 2013; Cook et al. 2013; Schoenfeld et al. 2014). Some recent studies have used electromyography (EMG) to assess whether muscular failure is synonymous with full motor unit recruitment (e.g. Sundstrup et al. 2012). This is very hazardous, as EMG primarily assesses voluntary activation, which is a composite measure of both motor unit recruitment and motor unit firing frequency. Additionally, during very fatiguing contractions, some heavily fatigued motor units are de-recruited, if only temporarily, which then allows a reduction in fatigue. Thus, at any given point in time within a fatiguing contraction, there may be a different combination of motor units that are recruited for generating the same level of force production. This adds an additional level of complexity.

Summary

In summary, training closer to muscular failure might be more effective than training further from muscular failure for hypertrophy on the basis that a greater neural signal occurs and consequently more motor units are recruited with closer proximity to muscular failure.

EFFECT OF PROXIMITY TO FAILURE ON MOLECULAR SIGNALING FOR HYPERTROPHY

Selection criteria

Population – any subjects

Intervention – single resistance training workouts, where >2 workouts involved training with different proximity to failure

Comparator – the other workout

Outcome – measures of molecular signaling associated with hypertrophy

Results

The following studies were identified: Burd (2010a), Burd (2012).

Findings

There are some indications that molecular signalling responses might be increased as a result of training closer to muscular failure. However, not all signalling molecules are elevated by increasing proximity to failure and the literature is still quite limited.

EFFECT OF PROXIMITY TO FAILURE ON MUSCLE PROTEIN SYNTHESIS

Selection criteria

Population – any subjects

Intervention – single resistance training workouts, where >2 workouts involved training with different proximity to failure

Comparator – the other workout

Outcome – measures of muscle protein synthesis

Results

The following studies were identified: Burd (2012).

Findings

There are some indications that muscular failure may be important for maximizing muscle protein synthesis post-workout, although the literature is very limited at present.

EFFECT OF MUSCULAR FAILURE ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >2 groups trained with different proximities to muscular failure (either by performing an identical number of repetitions but with an intra-set rest period or by stopping short of muscular failure in one group)

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Giessing (2014); Pareja-Blanco (2016).

Findings

These studies both reported a superior effect of training closer to muscular failure compared to training further from muscular failure. Training closer to muscular failure might therefore be superior for hypertrophy in this population.

EFFECT OF MUSCULAR FAILURE ON HYPERTROPHY (UNTRAINED)

Selection criteria

Population – untrained subjects

Intervention – resistance-training, where >2 groups trained with different proximities to muscular failure (either by performing an identical number of repetitions but with an intra-set rest period or by stopping short of muscular failure in one group)

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Schott (1995), Goto (2005), Sampson (2015).

Findings

Two of the studies reported a superior effect of training closer to muscular failure compared to training further from muscular failure, while one did not. The study that did not find a difference used a fast bar speed for the groups that did not train to muscular failure, and a slow bar speed for the group that trained to failure (Sampson & Groeller, 2015). Even so, training closer to muscular failure might therefore be superior for hypertrophy in this population.

It is widely assumed that training to muscular failure is best for maximizing gains in strength and size, during a strength training program. However, few studies have actually assessed this. Recently, one group of researchers tested whether training to muscular failure in every set of every workout would lead to superior gains in muscular strength and size, compared to two different groups who typically trained 2 reps short of failure. It is important to note that the study design was not ideal, as the groups who did not always train to failure used a maximal bar speed, while the group who always trained to failure used a slow concentric phase. And since all groups performed the same number of sets, the group who always trained to failure performed more volume than the groups who did not. Despite these limitations, however, this is an important study. And since it shows that training to failure all the time is not a superior approach, it casts doubt upon the idea that regularly training to failure is an essential element of hypertrophy programs.

A photo posted by Chris Beardsley (@chrisabeardsley) on

SECTION CONCLUSIONS

For untrained individuals, training closer to muscular failure appears to lead to greater hypertrophy. For trained individuals, training closer to muscular failure may also lead to greater hypertrophy.


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FREQUENCY

PURPOSE

This section explores whether training with a higher volume-matched frequency (i.e. number of training sessions per week) is more effective for hypertrophy than training with a lower volume-matched frequency. This is achieved by looking at long-term studies that compare whether a program where subjects train with different training frequencies and assessing their relative ability for increasing muscular mass or size.

DEFINITIONS

Training frequency is most commonly defined as the number of times per week that resistance training is performed, whether in relation to the whole body or a single muscle. We can use further definitions to be clearer about whether we are talking about the frequency of training a muscle group, or whether we are talking about the frequency of doing a workout. Muscle training frequency can be defined as the number of times that a muscle group is trained each week. In contrast, workout frequency can be defined as the number of workouts performed per week. This is an important consideration, as the same number of workouts can be performed by different trainees (e.g. 3 workouts per week) but they can be carried out in either a full body routine (all muscle groups worked 3 times per week) or a split routine (each muscle group only worked 1 time per week).

PROBLEMS

Controlling other variables when studying volume-matched training frequency is in theory relatively straightforward. A certain volume of training is identified and then allocated across two workout plans. The workout plan for one group involves a greater workload in a single workout than the other but performs fewer workouts over the course of the week. In practice, when working with trained subjects, it is slightly more complicated, as the only practical way to increase volume-matched training frequency is to train multiple times on the same day, which introduces a time-of-day effect. Training at different times of day has been found by some (Chtourou & Souissi, 2012) but not all (Sedliak et al. 2009) to affect muscular adaptations to training and may therefore be a confounding factor.

MECHANISMS OF HYPERTROPHY IN RELATION TO FREQUENCY

[Read more: mechanisms of hypertrophy]

Mechanical loading

The main stimulus for hypertrophy is thought to be the application of mechanical load to a joint, which results in tensile force within the muscle. Greater stimulus is thought to arise from more prolonged periods in which the muscle is subjected to this mechanical load. Within certain boundaries, training volume is closely tied to the resulting hypertrophic stimulus. However, there are good grounds for believing that there is a finite limit to both the volume that can be performed in a single workout (and over multiple sequential workouts) and the resulting hypertrophic stimulus, because of the need for adequate recovery. Thus, an optimal structure of volume-matched training frequency must exist, whereby individual workouts create the greatest possible stimulus.

Summary

In summary, training with a specific volume-matched frequency might be more effective than another volume-matched frequency because the distribution of the hypertrophic stimuli over the course of a training week are optimal in one case and not in the other. The extent to which the pattern of this distribution varies between individuals is unclear and may affect our ability to test this training variable accurately.

EFFECT OF FREQUENCY ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >2 groups trained with different volume-matched frequencies

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Häkkinen (1994), McLester (2000), Hartmann (2007), Schoenfeld (2015c).

Findings

Of these studies, 2 reported a superior effect of training with a higher volume-matched frequency compared to a lower volume-matched frequency. Training with a higher volume-matched frequency might therefore be superior for hypertrophy in this population.

EFFECT OF FREQUENCY ON HYPERTROPHY (UNTRAINED)

Selection criteria

Population – untrained subjects

Intervention – resistance-training, where >2 groups trained with different volume-matched frequencies

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Calder (1994), Benton (2011), Candow (2007), Arazi (2011).

Findings

Of these studies, 1 reported a superior effect of training with a lower volume-matched frequency compared to a higher volume-matched frequency, albeit only in one outcome measure, while the remainder reported no differences. Training with a higher volume-matched frequency is therefore unlikely to be superior for hypertrophy in this population.

SECTION CONCLUSIONS

For untrained individuals, altering volume-matched training frequency does not seem to have any effect on hypertrophy. For trained individuals, a higher volume-matched training frequency might to be superior to a lower volume-matched frequency for hypertrophy.


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REST PERIODS

PURPOSE

This section explores whether training with shorter inter-set rest periods is superior to training with longer inter-set rest periods for hypertrophy. This is achieved by looking at long-term studies that compare whether a program where subjects train with short inter-set rest periods (or reducing rest periods) is better than a program where subjects train with longer inter-set rest periods (or with non-reducing rest periods) for increasing muscular mass or size.

DEFINITIONS

Resistance training exercises are generally described as being performed in sets of repetitions, where a set is a number of repetitions performed in sequence. Where multiple sets of repetitions are performed, there is a rest between sets, called the inter-set rest period. The length of this inter-set rest period can be referred to as the inter-set rest period duration.

PROBLEMS

The main problem associated with altering rest period duration is controlling volume. As noted above, when reducing rest period duration, this leads to a reduction in the number of repetitions that can be performed in a single set. Thus, in order to control for volume while altering rest period duration while maintaining all sets to muscular failure, an additional set would be required in the condition with the shorter rest period duration.

MECHANISMS OF HYPERTROPHY IN RELATION TO REST PERIODS

[Read more: mechanisms of hypertrophy]

Mechanical loading

The main stimulus for hypertrophy is thought to be the application of mechanical loading to a joint, which results in tensile force within the muscle. Greater stimulus is thought to arise from more prolonged periods in which the muscle is subjected to this mechanical loading. Within certain boundaries, training volume is closely tied to the resulting hypertrophic stimulus. However, performing consecutive sets with the same relative load but shorter rest periods leads to fewer repetitions being performed than when longer rest periods are used (Miranda et al. 2009; Senna et al. 2009; Senna et al. 2011). Thus, unless additional sets are performed in order to match volumes, it is likely that using shorter rest periods will reduce volume and consequently reduce the stimulus provided by the mechanical load.

Metabolic stress

A secondary stimulus for hypertrophy is thought to be exercise-induced metabolic stress (Schoenfeld, 2010; Schoenfeld, 2013; Pearson and Hussain, 2014). There is a clear mechanism by which shorter rest periods could lead to increased metabolic stress, as muscular contractions above a certain (fairly low) threshold of maximum voluntary isometric contraction force prevent venous return. Since metabolic stress arises from the prevention of venous return, cell swelling and the buildup of metabolites such as blood lactate, intramuscular lactate, glucose and glucose-6-phosphate within the muscle in concert with the experience of a “muscle pump” (see review by Schoenfeld and Contreras, 2014), shorter rest periods would be expected to lead to greater metabolic stress and consequently greater hypertrophy, so long as all other factors remained constant. Previously, it was thought that a key factor in determining the extent to which hypertrophy occurred following a program of resistance training was the acute post-workout hormone response to training, which apparently results from greater metabolic stress (see reviews by Schoenfeld, 2013a; Henselmans and Schoenfeld, 2014). This idea has been termed the “hormone hypothesis” and has since been rejected by many researchers. It has been concluded that it is impossible to conclude on whether post-workout hormone responses have any effect on long-term hypertrophy but nevertheless suggested that any effect would likely be small in any event (Schoenfeld, 2013a; Henselmans & Schoenfeld, 2014).

Summary

In summary, training with shorter rest periods could either be more or less effective than with longer rest periods, depending on whether the stimulus from the mechanical load or the metabolic stress is greater, and on whether the short-rest and long-rest programs are volume-matched.

EFFECT OF REST PERIODS ON MOLECULAR SIGNALING FOR HYPERTROPHY

Selection criteria

Population – any subjects

Intervention – single resistance training workouts, where >2 workouts involved training with different rest periods

Comparator – the other workout

Outcome – measures of molecular signaling associated with hypertrophy

Results

The following studies were identified: Boroujerdi (2008), Rahimi (2010).

Findings

The majority of studies comparing the acute responses of different rest period durations have done so in respect of hormone levels rather than molecules within the key pathways. There are indications that IGF-1 is not affected by rest period duration, although some studies indicate that blood lactate is elevated by shorter rests.

EFFECTS OF REST PERIOD DURATION ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >2 groups trained with different rest period durations

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Ahtiainen (2005), Schoenfeld (2015d).

Findings

Of the 2 studies, 1 reported no differences between groups and 1 reported a superior benefit of longer rest periods. Training with a shorter rest period duration is unlikely to be superior for hypertrophy in this population, while training with a longer rest period duration may be helpful for maximizing gains in muscle mass, possibly because they allow the accumulation of greater volume loads.

EFFECTS OF REDUCING REST PERIOD DURATION ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >1 group trained with a fixed rest period duration and >1 group trained with a reducing rest period duration

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following study was identified: De Souza-Junior (2010).

Findings

This study reported no differences between groups. Training with a reducing rest period duration is unlikely to be superior for hypertrophy in this population.

EFFECTS OF REST PERIOD DURATION ON HYPERTROPHY (UNTRAINED)

Selection criteria

Population – untrained subjects

Intervention – resistance-training, where >2 groups trained with different rest period durations

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following 2 studies were identified: Buresh (2009), Villanueva (2014).

Findings

Of these studies, 1 reported a superior effect of longer rest period durations and 1 reported a superior effect of shorter rest period durations. Training with a shorter rest period duration is therefore unlikely to be superior for hypertrophy in this population.

SECTION CONCLUSIONS

For untrained individuals, rest period duration seems to make little difference to hypertrophy. For trained individuals, longer rests may be better, as they allow the accumulation of greater volume loads.


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RANGE OF MOTION

PURPOSE

This section explores whether training through larger ranges of motion (ROMs) leads to greater hypertrophy than training through smaller ROMs. This is achieved by looking at long-term studies that compare whether a program where subjects train through large ROMs is better than a program where subjects train through small ROMs for increasing muscular mass or size.

DEFINITIONS

Resistance training exercises are often described as being performed either through full ROMs or partial ROMs. For single-joint exercises, full ROMs can be defined as those in which the joint moves through its entire movement arc, subject to the constraints of passive tissues. Thus, full joint ROM is broadly equivalent to the muscle fully elongating. On the other hand, for multi-joint exercises, full ROMs are more difficult to define, as not all of the joints will necessarily move through their full movement arcs. For example, in a full ROM squat, the ankle joint does not move through its full ROM. Similarly, in a full ROM deadlift, the knee does not move through its full ROM. In the case of the deadlift, greater ROM than full ROM can be achieved by using a snatch grip or by using a platform to perform a deficit deadlift. Thus, for multi-joint exercises, full ROM may need to be defined conventionally as “greater ROM” rather than full ROM.

PROBLEMS

When studying the effect of any individual training variable on hypertrophy, a major problem is the extent to which other training variables can be fixed between the two groups being compared. The most important training variables to fix are those that have been found to have the biggest effect on hypertrophy (i.e. volume). In the case of ROM, it is relatively easy to equalize volume, particularly where volume is defined as the number of repetitions of the same relative load. In the research literature exploring the effect of ROM on hypertrophy, there are two types of study. One type compares the effect of training through an arbitrary, partial ROM in a machine exercise with a full ROM of the same exercise. The other explores the effect of training through a partial ROM in a free-weight exercise with a full ROM of the same exercise. In this latter type of study, the partial ROM variation enables the use of a much greater load than the full ROM equivalent because of the torque-angle curve. For example, in the conventional back squat, the torque-angle curve increases steeply with increasing hip or knee angle (i.e. increasing squat depth). This is because the external moment arms at the hip and knee increase steeply with increasing hip and knee angle (i.e. increasing squat depth), while the load stays the same. Arguably, performing free-weight exercises through a partial ROM is how individuals actually use smaller ROMs in resistance-training. Individuals generally stop slightly short of full squat depth. There is therefore a discrepancy between a portion of the research literature and general practice, indicating a lack of ecological validity.

MECHANISMS OF HYPERTROPHY IN RELATION TO RANGE OF MOTION

[Read more: mechanisms of hypertrophy]

Mechanical loading

The most common stimulus for hypertrophy is thought to be mechanical loading, which most often involves the development of tensile force in the muscles. A partial ROM allows greater absolute load to be lifted for the same relative load in many common barbell exercises. The greater absolute load is assumed to lead to greater tensile forces within the muscles. Indeed, for the squat, greater net joint moments have been recorded at greater angles of knee flexion (Bryanton et al. 2012). However, this assumption ignores the fact that net joint moments are the product of the barbell load and the external moment arm length. Consequently, although the barbell load is greater in the partial ROM condition, the external moment arm length is smaller. Thus, a smaller barbell load at full ROM can involve a similar or even a larger net joint moment compared to a larger barbell load at a partial ROM, which can translate to greater muscle forces (McMahon et al. 2014). Also, the greater distance through which the load is moved during during full ROM exercises leads to more work being performed in comparison with partial ROM exercises with the same absolute load (as work done = force x distance), and the greater absolute load used in most partial ROM exercises does not seem to compensate for this reduction in work done. Greater work done leads to greater training volume, which is associated with superior gains in muscle size.

Metabolic stress

A secondary stimulus for hypertrophy is thought to be exercise-induced metabolic stress (Schoenfeld, 2010; Schoenfeld, 2013). Whether ROM can affect metabolic stress is unclear. However, Miyamoto et al. (2013) reported that regional differences in vastus lateralis muscular hypertrophy are likely better explained by the regional differences in muscle oxygenation rather than regional differences in EMG activation. Indeed, several studies have reported that fatigue resistance is less and oxygen consumption is higher during isometric muscle actions in stretched positions in comparison with contracted positions for the quadriceps (De Ruiter et a. 2005; Kooistra et al. 2006; Debrosses et al. 2006; Kooistra et al. 2008). This may imply that greater metabolic demand is the key factor for the observed additive effects of stretch and contractile activity.

Molecular signalling for hypertrophy

The extent to which molecular signalling for hypertrophy differs between large and small ROM resistance training programs is unclear. Assuming that the differences between full and partial ROM exercises are stretch-mediated, then it may be useful to look at the differences in molecular signalling between resistance training programs at different muscle lengths but with similar ROMs. Additionally, it may be helpful to consider the effects of passive stretch on molecular signalling in respect of hypertrophy. McMahon et al. (2014) directly compared the long-term effects of two otherwise identical resistance training programs, where one used a stretched position and the other used a contracted position. It was found that IGF-1 levels increased to a greater extent following the resistance training program in the stretched position condition, which may have mediated the larger increase in muscle mass. Indeed, previous studies have observed increases in IGF-1 following stretched and hypertrophied muscles (Yang et al. 1996) and it has been proposed that locally-produced IGF-1 is a key mediating factor for stretch-mediated muscular hypertrophy (see reviews by Goldspink, 1999; De Deyne, 2001; Philippou et al. 2007; Philippou et al. 2009). There are at least three ways in which passive stretch could lead to molecular signalling events that ultimately cause muscle protein synthesis and hypertrophy: mechanoreceptors (possibly integrins, located in the costameres), growth factors (including IGF-1 and MGF) as discussed above, and stretch-activated ion channels, which appear to be mechanosensitive and cause alterations in ion flux (De Deyne, 2001). While the role of integrins has been implicated in the detection of mechanical tension during active muscle actions (see review by Schoenfeld, 2010), the roles of growth factors (see reviews by Goldspink, 1999; De Deyne, 2001; Philippou et al. 2007; Philippou et al. 2009) and stretch-activated ion channels (see review by Mohammad et al. 2011) potentially have a more specific mode of action in that they may only be activated following lengthening of the muscle. Insofar as the Akt-mTOR pathway is concerned, researchers have found that passive stretch leads to significant increases in the phosphorylation of Akt (Sakatomoto et al. 2003; Russ, 2008), although active stretch appears to cause greater increases (Russ, 2008), suggesting that passive stretch and contractile activity are additive in their effects through this pathway.

EFFECT OF ROM ON HYPERTROPHY (UNTRAINED)

Selection criteria

Population – untrained subjects

Intervention – resistance-training, where >2 groups trained with different ROM from one another

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Pinto (2012), Bloomquist (2013), McMahon (2013).

Findings

Of these studies, 2 reported a superior effect of larger ROM while the remainder reported no differences. Training with a larger ROM may therefore be superior for hypertrophy in this population.

SECTION CONCLUSIONS

For untrained individuals, a larger ROM appears to lead to greater hypertrophy than a shorter ROM. For trained individuals, there is unfortunately currently no evidence available.


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BAR SPEED (TIME UNDER TENSION)

PURPOSE

This section explores whether training with faster bar speeds is superior to training with slower bar speeds for hypertrophy. This is achieved by looking at long-term studies that compare whether a program where subjects train with fast bar speeds is better than a program where subjects train with slower bar speeds for increasing muscular mass or size.

DEFINITIONS

Resistance training exercises can be performed either maximally or sub-maximally. When performed maximally, the force-velocity relationship is relevant. The force-velocity relationship is the observation that when greater absolute moment is generated at a joint, the angular velocity of that joint must be lower. Force-velocity relationships at joints are largely exponential, with force decreasing very quickly with increasing angular velocity past a certain point. When performed sub-maximally, the force-velocity relationship is not relevant. In fact, as Fisher and Smith (2012) have noted, when performed to muscular failure, a greater number of repetitions are possible with faster bar speeds (i.e. shorter repetition durations) than with slower bar speeds (i.e. longer repetition durations). This in turn suggests that effort and fatigue levels are greater with slower bar speeds (i.e. longer repetition durations).

PROBLEMS

The force-velocity relationship is a serious confounding factor when comparing groups training with different maximal bar speeds. This is because the group training with the faster bar speed must use a lighter relative load. This means that relative load is different between the two conditions. However, when comparing two groups training with different sub-maximal bar speeds, the force-velocity relationship is normally not a problem. This is because the same relative load (for the bar speed) can be used in both cases. It is expected that in order to use slower sub-maximal bar speeds (longer repetition durations) the effort and fatigue are significantly greater than in faster sub-maximal bar speeds (shorter repetition durations. Therefore, it is anticipated that the absolute loads will be smaller for the same relative load in the slower sub-maximal bar speed conditions. Whether the same relative load is actually used is another matter. Indeed, the two studies reported below by Watanabe (Watanabe et al. 2013 and Watanabe et al. 2013a) compare two protocols that used different relative loads for the bar speed by using the same absolute load.

META-ANALYSES

Meta-analyses indicate that bar speed has no effect on hypertrophy during resistance training. Schoenfeld et al. (2015a) carried out a meta-analysis in trained and untrained subjects to compare the effects of fast and slow bar speeds (short and long repetition durations) during resistance training programs on gains in muscle size. It was found that there was no effect of bar speed (repetition duration) from durations ranging between 0.5 – 8.0 seconds.

MECHANISMS FOR HYPERTROPHY IN RELATION TO BAR SPEED

[Read more: mechanisms of hypertrophy]

Mechanical loading

The main stimulus for hypertrophy is thought to be the application of external mechanical load to a joint, which results in tensile force within the muscle. A greater relative load might be expected to require a activation of a greater number of motor units and thereby create a larger hypertrophic stimulus. However, since deliberately slower bar speeds (leading to longer repetition durations) involve lower relative loads, less force might be expected. This smaller force might lead to less hypertrophy. On the other hand, greater hypertrophic stimulus is thought to arise from more prolonged periods in which the muscle is subjected to mechanical load. Hence, greater time-under-tension subsequent to slower sub-maximal bar speeds (longer repetition durations) might be assumed to be more effective than faster sub-maximal bar speeds (shorter repetition durations), as they involve a longer duration of time during which the muscle is exposed to the stimulus.

Metabolic stress

A secondary stimulus for hypertrophy is thought to be exercise-induced metabolic stress (Schoenfeld, 2010; Schoenfeld, 2013). There is a clear mechanism by which longer repetition durations could lead to increased metabolic stress, as muscular contractions above a certain (fairly low) threshold of maximum voluntary isometric contraction force prevent venous return. Since metabolic stress arises primarily from the prevention of venous return and the consequent buildup of metabolites such as blood lactate, intramuscular lactate, glucose and glucose-6-phosphate within the muscle, longer repetition durations would be expected to lead to greater metabolic stress and consequently greater hypertrophy, so long as all other factors remained constant.

Summary

In summary, slower bar speeds (causing longer repetition durations) might be less effective than faster bar speeds (causing shorter repetition durations) because they involve lower relative loads. On the other hand, slower bar speeds might be more effective than faster bar speeds for hypertrophy on the basis that the tensile force in the muscle is longer in duration. Additionally, the longer period of time in which the muscle is subjected to metabolic stress when using slower bar speeds might also be expected to lead to increased hypertrophy.

EFFECT OF TIME UNDER TENSION ON MOLECULAR SIGNALING FOR HYPERTROPHY

Selection criteria

Population – any subjects

Intervention – single resistance training workouts, where >2 workouts involved training with different durations of time under tension

Comparator – the other workout

Outcome – measures of molecular signaling associated with hypertrophy

Results

The following studies were identified: Martineau (2002), Roschel (2011), Burd (2012).

Findings

There are some indications that a longer time under tension may enhance molecular signalling pathways for hypertrophy, although the literature is limited and confounded in human trials by muscular failure.

EFFECT OF TIME UNDER TENSION ON MUSCLE PROTEIN SYNTHESIS

Selection criteria

Population – any subjects

Intervention – single resistance training workouts, where >2 workouts involved training with different durations of time under tension

Comparator – the other workout

Outcome – measures of muscle protein synthesis

Results

The following studies were identified: Burd (2012).

Findings

There are some indications that time under tension may be important for maximizing muscle protein synthesis post-workout, although the literature is very limited at present.

EFFECT OF BAR SPEED ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >2 groups trained with different bar speeds (repetition durations) from one another

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Pareja-Blanco (2016), Pereira (2016).

Findings

These studies both used slightly unusual study designs. Pareja-Blanco et al. (2016) reported a superior effect of slower bar speeds, where the slower bar speed was achieved by training closer to muscular failure. The confounding effect of closer proximity to muscular failure in the slower group therefore makes this study hard to assess. Pereira et al. (2016) assessed slowing down only the lowering (eccentric) phase, and reported a superior effect in the slow group, even though both groups trained to muscular failure. Slowing down the eccentric phase may therefore lead to greater hypertrophy.

EFFECT OF BAR SPEED ON HYPERTROPHY (UNTRAINED)

Selection criteria

Population – untrained subjects

Intervention – resistance-training, where >2 groups trained with different bar speeds (repetition durations) from one another

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Young (1993), Keeler (2001), Neils (2005), Tanimoto (2006), Tanimoto (2008), Watanabe (2013), Watanabe (2013a).

Findings

Of these studies, 2 reported a superior effect of slower bar speeds while the remainder reported no differences. Training with a slower bar speed could possibly be superior for hypertrophy in this population but given the findings of meta-analyses, this seems unlikely.

SECTION CONCLUSIONS

For untrained individuals, deliberately slowing down bar speed to increase time under tension seems to make little difference to hypertrophy. For trained individuals, slowing down the eccentric phase seems to lead to greater hypertrophy.


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MUSCLE ACTION (VARIABLE)

PURPOSE

This section explores whether training with eccentric muscle actions is superior to training with concentric muscle actions while using isokinetic (i.e. variable) external resistance for hypertrophy. This is achieved by looking at long-term studies that compare isokinetic resistance training programs involving eccentric-only muscle actions are better than isokinetic resistance training programs involving concentric-only muscle actions for increasing muscular mass or size.

DEFINITIONS

[Read more: muscle function]

Muscles can be either active or passive, depending upon whether neural signals are sent to them. While being either active or passive, they can either lengthen, shorten, or remain the same length. Shortening active muscles are called concentric muscle actions, lengthening active muscles are called eccentric muscle actions, and when active muscles remain the same length, these are called isometric muscle actions. External resistance can initially be categorized into two overall categories: (1) external resistance that remains constant throughout a muscle action, (2) external resistance that varies throughout a muscle action. Within the first overall category of external resistance, the two main types are isoinertial and isometric. Isoinertial resistance is simply an object with mass that can be lifted. The mass remains the same at all time and any variation that occurs in how hard it is to lift throughout the joint range of motion depends entirely on the internal or external moment arms. Isometric external resistance is a subcategory of isoinertial resistance where the mass is too heavy to lift. Within the second overall category of external resistance, the two main types are variable and isokinetic. Variable resistance is simply where the resistance changes with joint range of motion in an unspecified way. Isokinetic resistance is essentially a subcategory of variable resistance but the way in which the resistance changes is so as to maintain a constant velocity throughout the joint range of motion. Isokinetic resistance thereby corrects for the internal and external moment arms at all points. Accommodating resistance is technically identically to isokinetic resistance in biomechanical definitions. However, in popular usage, it often refers to merely an approximation to isokinetic by the use of bands or chains. In such set-ups, the term variable resistance is correct.

PROBLEMS

Owing to the differences in energy cost and absolute force production between eccentric and concentric muscle actions, it is not an easy matter to control all of the other key variables, particularly volume and relative load. The use of isokinetic external resistance makes this issue even more complex, as force production varies constantly throughout a single repetition, across repetitions of the same set, and between conditions while the velocity does not.

META-ANALYSES

Meta-analyses suggested that there may be some benefits of performing eccentric muscle actions for maximizing hypertrophy. Roig et al. (2009) performed a meta-analysis to assess the effect of muscle action on hypertrophy. Roig et al. (2009) analysed 20 randomized controlled trials involving both isokinetic and isoinertial external resistance. They reported that when eccentric exercise was performed using higher relative loads, there was a significantly greater effect on hypertrophy, when muscular size was measured as muscle girth and there was a trend in the same direction when muscular size was measured using either MRI or CT scans.

MECHANISMS OF HYPERTROPHY IN RELATION TO MUSCLE ACTION

[Read more: mechanisms of hypertrophy]

Mechanical loading

There are several mechanisms through which eccentric-only training might lead to superior results to concentric-only or stretch-shortening cycle training, all of which involve an increase in mechanical loading. Firstly, eccentric-only training involves a lower energy cost for the same tensile forces being experienced within the muscle (e.g. Peñailillo, 2013). In this way, lifters are able to perform a greater volume of work while taxing their work capacity to the same degree (thereby involving a greater mechanical loading stimulus). A second point that is related to this is that eccentric-only training enables lifters to move a larger amount of weight than during concentric-only or stretch-shortening cycle muscle actions with the same percentage of 1RM (e.g. Flanagan, 2013; and Moir, 2013), which therefore involves greater absolute mechanical loading. These greater tensile forces arise because passive structures within the contractile elements of muscle fibers contribute to the mechanical tension that is developed by the active structures (Schoenfeld, 2010). Passive structures are thought to involve those external to the muscle fiber (i.e. the extracellular matrix) and also those internal to the muscle fiber (i.e. the giant molecule titin). Thirdly, eccentric muscle actions are thought to lead to greater exercise-induced muscle damage than concentric muscle actions, which may arise either because of the greater tension or because of the nature of the tension in that it is exerted while the muscle is lengthening. Exercise-induced muscle damage may be one mechanism by which hypertrophy is stimulated (see review by Schoenfeld, 2010). However, whether this factor is as important as has previously been reported is a matter of debate (see review by Schoenfeld, 2012). Muscle damage subsequent to eccentric muscle actions can be very small in nature or it can involve significant tears in the muscle. The phenomenon of muscle damage appears to bear some similarities with initial inflammatory responses to infection (Schoenfeld, 2010) insofar as the damaged muscle emits agents that attract macrophages and lymphocytes, which clear up the cellular debris. Agents are also released that lead to the release of growth factors regulating the proliferation and differentiation of satellite cells and consequently the repair of the muscle damage and the provision of new nuclei for the muscle fibers (Schoenfeld, 2010).

Summary

In summary, eccentric muscle actions might be more effective than concentric muscle actions for hypertrophy because they (1) allow greater mechanical tension to be developed, (2) permit a greater volume of training to be performed, and (3) lead to greater muscle damage.

EFFECT OF MUSCLE ACTION ON MOLECULAR SIGNALING FOR HYPERTROPHY

Selection criteria

Population – any subjects

Intervention – single resistance training workouts, where >2 workouts involved training with different muscle actions

Comparator – the other workout

Outcome – measures of molecular signaling associated with hypertrophy

Results

The following studies were identified: Martineau (2001), Eliasson (2006), Cuthbertson (2006), Vissing (2013), Rahbek (2014), Hyldahl (2014).

Findings

Eccentric muscle actions may lead to different molecular signalling responses for hypertrophy than concentric muscle actions, both irrespective of muscle fiber type, and specifically in type II muscle fibers.

EFFECT OF MUSCLE ACTION ON MUSCLE PROTEIN SYNTHESIS

Selection criteria

Population – any subjects

Intervention – single resistance training workouts, where >2 workouts involved training with different muscle actions

Comparator – the other workout

Outcome – measures of muscle protein synthesis

Results

The following studies were identified: Moore (2005), Cuthbertson (2006), Rahbek (2014).

Findings

Eccentric muscle actions may lead to greater levels of acute muscle protein synthesis but this may depend on whether relative load is matched. Matched absolute loads tend to display no differences between conditions. This may imply that absolute mechanical loading is the key factor driving the difference in muscle protein synthesis.

EFFECT OF MUSCLE ACTION ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >1 group trained using predominantly or exclusively eccentric muscle actions, and >1 group trained predominantly or exclusively using concentric muscle actions, and where the external resistance used in all compared groups was isokinetic

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following study was identified: Seger (1998).

Findings

This study reported a superior effect of eccentric muscle actions for one outcome measure. Training with an eccentric muscle action while using this type of external resistance could therefore be superior for hypertrophy in this population.

EFFECT OF MUSCLE ACTION ON HYPERTROPHY (UNTRAINED)

Selection criteria

Population – untrained subjects

Intervention – resistance-training, where >1 group trained using predominantly or exclusively eccentric muscle actions, and >1 group trained predominantly or exclusively using concentric muscle actions, and where the external resistance used in all compared groups was isokinetic

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Komi (1972), Mayhew (1995), Higbie (1996), Hortobagyi (1996), Hortobagyi (2000), Farthing (2003), Nickols-Richardson (2007), Blazevich (2007), Moore (2012), Váczi (2014), Cadore (2014), Kim (2014).

Findings

Of these studies, 5 reported a superior effect of eccentric muscle actions while 1 reported a superior effect of concentric muscle actions. Training with an eccentric muscle action may therefore be superior for hypertrophy in this population while using this type of external resistance, although there are conflicting reports.

SECTION CONCLUSIONS

For trained individuals using variable-load external resistance, there is limited evidence that eccentric muscle actions might be superior to concentric muscle actions. For untrained individuals using variable-load external resistance, there is conflicting evidence that eccentric muscle actions might be superior to concentric muscle actions.


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MUSCLE ACTION (CONSTANT LOAD)

PURPOSE

This section explores whether training with eccentric muscle actions is superior to training with concentric muscle actions while using isoinertial external resistance (i.e. constant load) for hypertrophy. This is achieved by looking at long-term studies that compare whether isoinertial resistance training programs involving eccentric-only muscle actions are better than isoinertial resistance training programs involving concentric-only muscle actions for increasing muscular mass or size.

DEFINITIONS

See previous section: Muscle action (isokinetic)

MECHANISMS FOR HYPERTROPHY

See previous section: Muscle action (isokinetic)

PROBLEMS

Owing to the differences in energy cost and absolute force production between eccentric and concentric muscle actions, it is not an easy matter to control all of the other key variables, particularly volume and relative load. When comparing eccentric and concentric muscle actions across two groups, there are two common options for equating the load used in each group. Either the same absolute load can be used in both groups or the same relative load can be used in both groups. Another, less-common option is to use an arbitrary, heavier load in the eccentric group. Where the same absolute load is used in both eccentric and concentric groups, this means that the relative load is lower in the eccentric condition (as muscles are stronger during eccentric muscle actions than during concentric muscle actions). Thus, relative load becomes a confounding factor in the investigation. Where the same relative load is used, this eliminates relative load as a confounding factor. However, if the same set and repetition scheme is then employed between the eccentric and concentric groups, then (depending on how you define volume) this leads to an excess of volume being performed in the eccentric condition than in the concentric condition (because the absolute load is greater).

EFFECT OF MUSCLE ACTION ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >1 group trained using predominantly or exclusively eccentric muscle actions, and >1 group trained predominantly or exclusively using concentric muscle actions, and where the external resistance used in all compared groups was constant load (isoinertial)

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following study was identified: Vikne (2006).

Findings

This study reported a significant benefit of eccentric muscle actions compared to concentric muscle actions. Training with eccentric muscle actions may therefore be superior for hypertrophy in this population with this type of external resistance but the literature is very limited.

EFFECT OF MUSCLE ACTION ON HYPERTROPHY (UNTRAINED)

Selection criteria

Population – untrained subjects

Intervention – resistance-training, where >1 group trained using predominantly or exclusively eccentric muscle actions, and >1 group trained predominantly or exclusively using concentric muscle actions, and where the external resistance used in all compared groups was constant load (isoinertial)

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Jones (1987), Ben-Sira (1995), Reeves (2009), Smith (1995), Farup (2013), Franchi (2014), Farup (2014).

Findings

All but one of these studies reported no differences between groups. The remaining study reported a significant benefit of concentric muscle actions. Training with eccentric muscle actions does not therefore seem to be superior for hypertrophy in this population with this type of external resistance.

SECTION CONCLUSIONS

For trained individuals using constant-load external resistance, there is limited evidence that eccentric muscle actions might be superior to concentric muscle actions. For untrained individuals using constant-load external resistance, there does not seem to be any difference between eccentric and concentric muscle actions.


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PERIODIZATION

PURPOSE

This section investigates whether periodization is effective for hypertrophy. This is achieved by looking at long-term studies that compare whether a periodized program is better than a non-periodized program for increasing muscular mass or size. The section also investigates which periodized program is best for muscular hypertrophy. This is achieved by looking at long-term studies that compare different types of periodized program and their effects on either muscle mass or size.

DEFINITIONS

Introduction

The term “periodization” has historically been notoriously difficult to define with any degree of precision or consensus. However, in this analysis, periodization will be defined as “the structure of a training program, where this training program varies over time, either linearly, non-linearly, or in blocks, in order to maximize the results of the athlete.” In contrast, a non-periodization training program will be defined either as a non-varied program or a program that varies randomly. Any training variable can be periodized (i.e. exercise selection, relative-load, volume, frequency, range-of-motion, proximity to failure, rest periods, etc.). However, in practice the two most commonly-varied training variables are relative load and volume. Typically, volume is reduced while relative load is increased and vice versa.

Periodization types

Periodization types fall into three main categories: linear, non-linear, and block. Linear periodization involves sequential alteration of key training variables over time. Non-linear periodization involves altering training variables from day-to-day or from week-to-week such that all training variables are used similarly within short periods of time. Block periodization involves training for a specific goal in successive, additive cycles. Linear periodization is the traditional and earliest form of periodization. It was originally proposed by Matveyev in the 1950s and involves a steady progression from high-volume, low-relative load training at the start of the program through to low-volume, high-relative load training at the end. A variant of linear periodization is reverse linear periodization in which the opposite sequence is followed. Non-linear periodization, which encapsulates methods known as undulating periodization and conjugate periodization, involves a less sequential change in training variables than linear periodization over the course of a training cycle. In non-linear periodization, workouts are arranged with training variables being altered across multiple workouts over short periods. This can occur from day-to-day over the course of a single week of workouts (daily undulating periodization) or from week-to-week over the course of several weeks of workouts (weekly undulating periodization). While volume and relative load are most commonly investigated and manipulated over the course of periodized programs, there is no reason why exercise selection cannot be changed in the same way (e.g. as in the Westside method). Block periodization was proposed by Verkoshansky (1998) and involves cycles of sequential training designed to achieve a specific goal. Each block is intended to be the foundation for the next one. Depending on the terminology used, a typical sequence of cycles would be accumulation, transformation and realization, which are elsewhere called hypertrophy, maximal strength and power. The progression from high-volume, low-relative load to lower-volume and higher-relative loads makes it easy to confuse with linear periodization but the premise behind block periodization is different and involves a focus on the goal of the training cycle rather than just the sets and reps. For a discussion of the differences between block and traditional linear periodization, see Issurin (2008).

PROBLEMS

Periodization is very difficult to study in practice, making our ability to draw conclusions from the literature limited. Many researchers and coaches have drawn attention to the limitations of the current literature (e.g. Cissik, 2008), which has not kept pace with research in other areas, such as the effects of certain training variables on strength gains (e.g. relative load, volume, etc.). Primarily, Cissik (2008) observed that it is problematic that the majority of available studies are short-term in nature (approximately the duration of an academic semester), use non-athletic college populations, and primarily involve strength training modalities only. Cissik therefore suggested that this makes it difficult to the current periodization research to athletic populations who structure their training plans over years and performed concurrent training modalities. For the purposes of applying the available research to the achievement of strength gains during recreational resistance-training, however, these are not large concerns. More concerning for the application of the available research to recreational resistance-training was raised by Kiely (2012), who pointed out most experimental designs exploring periodization have actually simply compared varied with non-varied interventions. Thus, such studies simply demonstrate that variation is important, and not that periodization is the best way of providing this variation. Therefore, until a high quality study compares a randomized program with a periodized program and with a non-varied program, we will continue to lack an understanding of whether variation or structured periodization are of greater importance.

MECHANISMS OF HYPERTROPHY IN RELATION TO PERIODIZATION

[Read more: mechanisms of hypertrophy]

General Adaptation Syndrome

The two primary mechanisms for bringing about hypertrophy are mechanical loading and metabolic stress. It is unclear precisely how periodization helps to maximize either of these two mechanisms. Although it seems that periodization was adopted prior to the existence of an evidence base, researchers have since proposed at least two plausible mechanisms to support existing practice. The majority of commentators on periodization reference Selye’s General Adaptation Syndrome (see further Haff, 2004). Indeed, it does seem logical that by incorporating changes to the program variables (e.g. relative load, volume, exercises, etc.), this would cause the neuromuscular systems to be exposed to unaccustomed stressors. However, as noted above, it is unclear precisely how this relates to mechanical loading or metabolic stress. Similarly, it seems sensible that by failing to introduce variation, continued improvements are likely to cease. However, this mechanism only suggests that variability is necessary and does not account for the proposed need for structure within the concept of periodization.

Sequenced potentiation

In addition to the General Adaptation Syndrome, researchers working in the area of periodization also refer to the mechanism of sequenced potentiation (see further Haff, 2004). Sequenced potentiation suggests that building a foundation of strength with heavy loads allows individuals to maximize the gains they can achieve from power-training with lighter loads. Similarly, hypertrophy-training might be achieved more quickly in stronger individuals, where a foundation of strength has already been built. This interesting idea may support the idea of block periodization but does not lend strong conceptual support to other methods, such as traditional linear periodization or non-linear methods that vary loading schemes very regularly.

EFFECTS OF PERIODIZED VS. NON-PERIODIZED PROGRAMS ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >1 group trained using a recognised periodization model and the other group did not use a periodization model

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Baker (1994), Monteiro (2009).

Findings

Of these studies, neither found any differences between groups. Using periodization does not appear to lead to superior hypertrophy in this population.

EFFECTS OF LINEAR VS. NON-LINEAR PROGRAMS ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >1 group trained using a linear periodization model and >1 group trained using a non-linear periodization model

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Baker (1994), Monteiro (2009), Prestes (2009), Harries (2015).

Findings

Of these studies, none found any differences between groups. Using non-linear periodization does not appear to lead to superior hypertrophy to linear periodization in this population.

EFFECTS OF LINEAR VS. REVERSE LINEAR PROGRAMS ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >1 group trained using a linear periodization model and >1 group trained using a reverse linear periodization model

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following study was identified: Prestes (2009).

Findings

This study found that linear periodization was superior to reverse linear periodization. Using linear periodization could therefore lead to superior hypertrophy to reverse linear periodization in this population.

EFFECTS OF LINEAR VS. BLOCK PROGRAMS ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >1 group trained using a linear periodization model and >1 group trained using a block periodization model

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following study was identified: Bartolomei (2014).

Findings

This study found no differences between groups. Using block periodization may therefore be similarly effective to linear periodization in this population.

EFFECTS OF PERIODIZED VS. NON-PERIODIZED PROGRAMS ON HYPERTROPHY (UNTRAINED)

Selection criteria

Population – untrained subjects

Intervention – resistance-training, where >1 group trained using a recognised periodization model and the other group did not use a periodization model

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Stone (1981), Souza et al. (2014).

Findings

Of these studies, 1 found a benefit of periodization and 1 found no differences between groups. Using periodization could therefore lead to superior hypertrophy to no periodization in this population.

EFFECTS OF LINEAR VS. NON-LINEAR PROGRAMS ON HYPERTROPHY (UNTRAINED)

Selection criteria

Population – untrained subjects

Intervention – resistance-training, where >1 group trained using a linear periodization model and >1 group trained using a non-linear periodization model

Comparator – baseline performance or a non-training control group

Outcome – at least one reliable measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Kok (2009), Simão (2012), De Lima (2012), Souza et al. (2014).

Findings

Of these studies, only 1 found a superior benefit of non-linear periodization over linear periodization, while the remainder found no differences between groups. Using non-linear periodization could possibly lead to superior hypertrophy to linear periodization in this population.

SECTION CONCLUSIONS

For trained individuals, periodization makes little difference for hypertrophy. There is limited evidence to suggest that reverse linear is worse than linear but linear and non-linear approaches appear to have equal merit. For untrained individuals, there are conflicting indications that periodization might be superior to non-periodization and that non-linear might be superior to linear.


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EXERCISE SELECTION

PURPOSE

This section explores how exercise selection affects hypertrophy. This is achieved by looking at long-term studies comparing the long-term effects of two or more programs on increases in muscular size, where the choice of exercise is different in each program.

DEFINITIONS

Addressed in this section are the following categories of exercise selection:

  • The number of joints (single vs. multi-joint exercises)
  • Exercise variety for the same body part (single vs. multiple exercises)

The number of joints can be explored by comparing the long-term effects on muscular size of training using a single-joint exercise for a muscle group with a similar program incorporating a multi-joint exercise that works the same muscle group. Exercise variety can be explored by comparing the long-term effects on muscular size of training using a single exercise for a muscle group with a similar program incorporating multiple exercises for the same muscle group. The variety of exercises can be obtained by using a range of the same type of exercise (i.e. all multi-joint exercises) or by comparing the use of multi-joint exercises alone with the use of multi-joint and single-joint exercises together.

MECHANISMS OF HYPERTROPHY IN RELATION TO EXERCISE SELECTION

Number of joints

[Read more: mechanisms of hypertrophy]

In general, multi-joint exercises (such as the bench press) involve many muscle groups, including proximal muscles such as the pectoralis major, as well as distal muscles such as the the triceps brachii. It has been suggested that training using single-joint exercises (like triceps extensions) might be better for the distal muscles than training using multi-joint exercises (like the bench press) on the basis that the muscles are expected to be more highly activated during these isolation exercises. To support this contention, it has been noted that during multi-joint exercises like the bench press, the muscle activity of the triceps brachii is often lower than the muscle activity of the other prime movers (Gentil et al. 2007; Brennecke et al. 2009). However, this has not uniformly been reported, and some researchers have found the opposite result (Clemons and Aaron, 1997). Similarly, some researchers have found that single-joint exercises (such as the dumbbell fly) do not activate the intended muscle as much as a multi-joint exercise equivalent (such as the bench press) (Welsch et al. 2005). It is therefore unclear whether single-joint exercises are likely to be superior to multi-joint exercises for developing the same muscles, where all other variables remain equal. Another concern is whether the use of multi-joint and single-joint exercises allows the same training frequency. Soares et al. (2015) found that single-joint exercise cause greater muscle soreness and require longer to recover from than multi-joint exercises.

It has been suggested that training certain muscles using single-joint exercises might be superior to multi-joint exercises as they might allow greater muscular activation. However, this is not uniformly observed in research. Therefore, it is unclear whether single-joint or multi-joint exercises are superior for hypertrophy.

Exercise variety

[Read more: mechanisms of hypertrophy]

Within-muscle regional hypertrophy may be one cause of differences in training programs using different degrees of exercise variety. Within muscle-group hypertrophy may be another factor differentiating between programs with greater or lesser exercise variety, as some exercises have been found to activate some muscles within a group to a greater extent than others. Regarding regional hypertrophy, there is long-term evidence that training with a different range of motion (ROM) or a different external resistance type can affect the extent to which muscular size is gained in different parts of the same muscle. Exercise ROM and external resistance type affect the net joint moment at different points in a joint ROM when using the same exercise. Different exercises similarly display different joint moments at different joint ROMs. Therefore, is is unsurprising that there is acute evidence that different regions of the same muscle are stimulated by different exercises (Mendiguchia et al. 2013), and differences in regional hypertrophy likely occur with different exercises.

Training with a larger exercise variety is expected to bring about greater gains in muscle mass than training with a smaller exercise variety, most likely because of differences in regional hypertrophy or greater hypertrophy across all of individual muscles within a single muscle group.

EFFECT OF EXERCISE JOINT NUMBER ON HYPERTROPHY (UNTRAINED)

Selection criteria

Population – untrained subjects

Intervention – resistance-training, where >1 group trained predominantly or exclusively using single-joint exercises and >1 group trained predominantly or exclusively using multi-joint exercises

Comparator – baseline performance or a non-training control group

Outcome – any measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following study was identified: Gentil (2015).

Findings

The researchers found that there were no differences between single-joint and multi-joint exercises for increasing muscle thickness.

EFFECT OF EXERCISE VARIETY ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >1 group trained predominantly or exclusively using limited exercise variety and >1 group trained predominantly or exclusively using a greater exercise variety (i.e. >1 additional exercise to the other group)

Comparator – baseline performance or a non-training control group

Outcome – any measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Rogers (2000), Silvestre de França (2015).

Findings

These studies compared the effects of 2 multi-joint upper body exercises with 2 multi-joint and 2 single-joint upper body exercises and found no differences between groups. This suggests that increasing exercise variety by incorporating single-joint exercises into a multi-joint training program does not increase gains in muscular size.

EFFECT OF EXERCISE VARIETY ON HYPERTROPHY (UNTRAINED)

Selection criteria

Population – untrained subjects

Intervention – resistance-training, where >1 group trained predominantly or exclusively using limited exercise variety and >1 group trained predominantly or exclusively using a greater exercise variety (i.e. >1 additional exercise to the other group)

Comparator – baseline performance or a non-training control group

Outcome – any measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Gentil (2013), Fonseca (2014).

Findings

Both Gentil et al. (2013) compared the effects of 2 multi-joint upper body exercises with 2 multi-joint and 2 single-joint upper body exercises and found no differences between groups. However, Fonseca et al. (2014) compared the effects of 3 multi-joint exercises (squat, lunge, deadlift) vs. 1 multi-joint exercise (squat) and found that the greater exercise variety was superior when comparing individual muscles within the quadriceps muscle group. This may imply that the benefits of exercise variety are primarily observed when using multi-joint exercises.

SECTION CONCLUSIONS

For trained individuals, it is unclear whether single-joint exercises lead to different gains in muscular size to multi-joint exercises. Adding single-joint exercises to an existing program of multi-joint exercises does not appear to enhance overall gains in muscular size (but might affect where gains occur).

For untrained individuals, single-joint exercises appear to lead to similar gains in muscular size to multi-joint exercises. Adding single-joint exercises to an existing program of multi-joint exercises does not appear to enhance gains in muscular size (but might affect where gains occur). Using several multi-joint exercises appears to cause more consistent hypertrophy within a muscle group than using one multi-joint exercise.


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ADVANCED TECHNIQUES

PURPOSE

This section explores how different advanced bodybuilding techniques affect hypertrophy. This is achieved by looking at long-term studies comparing the effects of two or more programs on gains in muscular size, where an advanced technique is used in one program but not in another.

USAGE

Popular usage

Bodybuilders make use of a range of advanced or specialized techniques that are intended to enhance long-term gains in muscle mass during resistance training programs. Surveys (e.g. Hackett et al. 2013) have reported that bodybuilders most commonly use:

  • Pyramids (progressions from lighter loads with higher repetitions to heavier loads with fewer repetitions overall several sets)
  • Supersets (two exercises performed in alternating sequence)
  • Forced repetitions
  • Partial repetitions
  • Negative repetitions (eccentric muscle actions)

The use of partial repetitions and negative repetitions will not be discussed in this section, as they are training variables in their own right (range of motion and muscle action) and are therefore covered in their own sections above. The most common techniques used by bodybuilders that have also been explored in the literature are: pre-exhaustion, the rest pause technique, drop sets, supersets, and forced repetitions.

MECHANISMS OF HYPERTROPHY IN RELATION TO ADVANCED TECHNIQUES

[Read more: mechanisms of hypertrophy]

Pre-exhaustion

INTRODUCTION

Pre-exhaustion involves performing a set of one exercise directly before a set of another exercise, where at least one muscle is used in both exercises. Commonly, pre-exhaustion is used with a single-joint exercise prior to a multi-joint exercise to help target one specific muscle across the two exercises. For example, a biceps curl might be performed directly prior to a lat pull-down to help pre-fatigue the biceps brachii (Vilaça-Alves et al. 2014), a knee extension exercise might be performed prior to a leg press to help pre-fatigue the quadriceps (Augustsson et al. 2003), and a pec deck or dumbbell fly exercise might be performed directly prior to a chest press or bench press to help pre-fatigue the pectoralis major (Gentil et al. 2007; Brennecke et al. 2009).

MECHANISMS

Pre-exhaustion is intended to increase muscle activation to a greater extent than conventional resistance training, in certain target muscles. However, it may also have an impact on the volume performed in the workout. The extra set performed as a pre-exhaustion technique increases volume, but the fatigue incurred causes a reduction in the volume of the main set.

MUSCLE ACTIVATION

Acute investigations of pre-exhaustion techniques have often found that muscle activation of the target muscle is not higher after using the pre-exhaustion technique compared to conventional resistance training, at least in the prime movers that are shared by the two exercises (Augustsson et al. 2003; Gentil et al. 2007; Brennecke et al. 2009). However, there are indications that muscle activation of the prime movers of the non-shared muscles is increased. For example, when performing either a dumbbell fly or pec deck exercise before the bench press, the muscle activation of the triceps brachii is increased substantially (Augustsson et al. 2003; Gentil et al. 2007).  Pre-exhaustion may therefore be helpful for shifting the emphasis of an exercise, although this would make it less useful for bodybuilders adhering to a strict body part split.

VOLUME LOAD

Some acute investigations have reported that the pre-exhaustion technique leads to fewer repetitions being performed in the main exercise (Augustsson et al. 2003; Gentil et al. 2007; Brennecke et al. 2009; Vilaça-Alves et al. 2014), although this is not observed across all exercises where repetitions in both the pre-exhaustion exercise and the main exercise are measured (Gentil et al. 2007). Nevertheless, this reduction in repetitions in the main exercise may lead to overall lower volume load performed in a workout, which would be disadvantageous.

CONCLUSIONS

The pre-exhaustion technique increases the level of muscle activation in the non-shared prime mover muscle in the main exercise, but does not increase the muscle activation of the shared prime movers. It may therefore be helpful for shifting the emphasis of an exercise. In addition, since pre-exhaustion training may lead to lower volume in the main set, pre-exhaustion training may be unhelpful for maximizing hypertrophy.

Rest pause technique

INTRODUCTION

The rest pause technique involves implementing a short rest between repetitions of a single set (i.e. an intra-set rest). The length of the intra-set rest period can vary. Relatively long intra-set rest periods of 20 seconds have most commonly been investigated (Lawton et al. 2006; Marshall et al. 2012; Giessing et al. 2014) but studies have also explored the use of even longer intra-set rest periods (Lawton et al. 2006; Iglesias et al. 2010; Oliver et al. 2013) and also much shorter intra-set rest periods (Keogh et al. 1999). In strength and conditioning, the rest pause technique is usually called “cluster” training (Haff et al. 2008).

MECHANISMS

Research into the mechanisms by which the rest pause technique could be effective suggests that it is primarily effective as it allows the use of heavier loads and greater volumes than conventional straight set training. This greater volume load is likely possible as the short intra-set rests permit recovery from fatigue between repetitions (Denton et al. 2006; Girman et al. 2014). However, there are also some indications that muscle activation might be greater when using rest pause technique compared to a conventional straight set technique (Marshall et al. 2012).

VOLUME LOAD

The ability to use higher volume loads when using intra-set rest periods has been confirmed in both acute (Lawton et al. 2006; Iglesias et al. 2010) and in some long-term studies (Giessing et al. 2014).

CONCLUSIONS

Since many researchers have found that rest pause training permits a greater volume load to be performed (because the intra-set rest periods permit recovery from fatigue), and since volume is a key factor driving greater increases in muscle mass, this indicates that rest pause training could be beneficial for maximizing hypertrophy.

Drop sets

INTRODUCTION

Drop sets involve performing a single set of an exercise with a given load and then immediately lowering the load (typically either by changing the setting on a machine or selecting a lighter dumbbell) before performing an additional set or sets. Drop sets are typically performed for at least 3 total sets. For example, Bentes et al. (2012) explored the effects of 3 total sets (10RM, 80% of 10RM, and 60% of 10RM) and Simola et al. (2015) explored the effects of 4 sets to muscular failure with progressively reducing loads (85%, 70%, 55% and 40% of 1RM).

MECHANISMS

Little research has been performed into the mechanisms by which drop sets might be effective and no obvious pathway has been identified as the primary target of interest. Schoenfeld (2011) suggested that any superior effects could be attributed to greater muscular fatigue and metabolic stress resulting from the extended period of time under tension. Such effects may differ between trained and untrained individuals, however (Goto et al. 2016). Equally, it is also possible that drop sets may permit a greater volume of work to be performed, by modulating the load used to suit the current state of fatigue and thereby making the workout more efficient.

VOLUME LOAD

In one of the few studies performed in this area, Bentes et al. (2012) compared 4 different protocols, all using drop sets, and reported that when drop sets were used with the main exercise (bench press) this led to greater overall work being done than when drop sets were used with a pre- or post-exhaustion exercise (dumbbell fly). This suggests that where drop sets are performed, they should be used with multi-joint exercises involving larger absolute loads in order to maximize work done. Simola et al. (2015) found that tensiomyography changes were greater when using drop sets than when using some other resistance training techniques, which they interpreted might imply the presence of greater muscle forces or greater fatigue. Since the predictive value of tensiomyography is still unclear, the implications of this finding are uncertain.

CONCLUSIONS

No mechanism has been identified as the primary possibility for explaining why drop sets might be effective. The longer time spent under tension likely leads to greater fatigue, while multiple, repeated sets could lead to greater volume performed. Either of these could potentially stimulate greater muscle growth. Therefore, it is unclear whether drop sets are beneficial for maximizing hypertrophy.

Supersets

INTRODUCTION

Supersets can be performed either as agonist supersets or antagonist supersets. In agonist supersets, two exercises that target the same prime movers are performed in an alternating fashion. In antagonist supersets, which are more common, two exercises that target opposing prime movers (e.g. back and chest muscles) are performed in an alternating fashion. Supersets are typically repeated for as many times as would otherwise be desired for a single or multiple set protocol. For example, Paz et al. (2015) used a protocol of 3 sets of chest press and 3 sets of seated row performed in an alternating manner, while Paz et al. (2013) used a single set of chest press and a single set of seated row performed in an alternating manner.

MECHANISMS

Little research has been performed into the mechanisms by which antagonist supersets might be effective. Supersets might permit a greater volume, volume load, or work to be performed. Even so, other suggestions have been made. Schoenfeld (2011) once proposed that the shorter rests might also lead to greater fatigue and consequently increased hypertrophy. However, new evidence from long-term trials indicates that shorter rest periods do not increase gains in muscle mass, but that longer rest periods are in fact superior (Schoenfeld et al. 2015d). Nevertheless, there are indications that supersets increase fatigue, as they have been observed to lead to greater blood lactate (Kelleher et al. 2010) and such elevations may increase metabolic stress and consequently increase gains in muscular size.

VOLUME LOAD

Many researchers have found that a greater volume can be performed using supersets (Robbins et al. 2010; Paz et al. 2013; De Freitas et al. 2014; Paz et al. 2015) and also greater muscle activation of certain muscles (De Freitas et al. 2014), although not all researchers have confirmed this finding (Carregaro et al. 2013).

Traditional strength training involves performing multiple sets of a single exercise before starting a second exercise. Superset training involves alternating between sets of two different exercises in sequence. – Supersets can be done in several ways. They can involve either the same prime movers (called agonist supersets) or they can involve opposing muscle groups (called antagonist supersets). They can also be performed with minimal rest between supersets, or with normal inter-set rest periods. – Agonist supersets with minimal rest between sets are generally used to increase muscular fatigue in specific muscles. Antagonist supersets with normal inter-set rest periods are thought to (1) allow more work to be done in less time, or (2) permit greater volume loads in the same overall workout time, because of longer rest period durations between like exercises. – This study confirmed the value of antagonist supersets with normal inter-set rest periods for maximizing volume load, which may be valuable during hypertrophy training blocks.

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Interestingly, it appears that the precise order of exercises within an antagonistic superset might affect the overall volume that can be achieved in a single training session (Balsamo et al. 2012). Care should therefore be taken to ensure that the optimal order of exercises within a superset is obtained. The increase in work might result from improved acute force production, possibly through improved co-ordination between agonist and antagonist muscle groups (Baker & Newton, 2005). However, the exact effects of performing agonist-antagonist supersets on acute force production is unclear, with some investigations finding reduced force production in the agonist following agonist-antagonist superset training (Maynard and Ebben, 2003) and some reporting a potentiated response (Kaminura and Takenaka, 2007).

CONCLUSIONS

Since many researchers have found that supersets permit greater volume to be performed (possibly because the agonist-antagonist pairing allows a potentiation of force production), and since volume is a key factor driving greater increases in muscle mass, this indicates that supersets could be beneficial for maximizing hypertrophy.

Forced repetitions

INTRODUCTION

Forced repetitions are those where a spotter helps the lifter carry out part or all of a repetition towards the end of a set. Forced repetitions can be performed in two main ways. Firstly, they can be performed in variable numbers to reach a predetermined total number of repetitions in a set (e.g. Drinkwater et al. 2007). Alternatively, they can be performed as a set number of forced repetitions per set, so as to meet a predetermined intensity threshold (Giessing, 2007).

MECHANISMS

Little research has been performed into the mechanisms by which forced repetitions could be effective. it has been proposed that higher post-exercise growth hormone levels might be responsible for any superior effects observed when using this type of training technique and that this might be mediated by greater muscular fatigue and metabolic stress (Schoenfeld, 2011). Ahtiainen et al. (2003) observed that acute growth hormone levels at 30 minutes post-exercise were higher after a workout involving forced repetitions than after a comparable workout without forced repetitions. However, the relationship between acute post-exercise growth hormone levels and long-term muscular hypertrophy is unclear and although some early studies identified an association (McCall et al. 1999; Häkkinen et al. 2003), other more recent investigations have not (Mitchell et al. 2013). Additionally, Boroujerdi & Rahimi (2008) observed that using a shorter rest period duration led to greater post-exercise growth hormone levels than using longer rest periods during forced repetition training. Since rest period duration is now known to have little effect on long-term gains in muscle mass, it is unlikely that altering growth hormone levels is responsible for any benefit of forced repetition training.

CONCLUSIONS

Since short rest periods cause elevated post-exercise growth hormone response and yet do not increase long-term gains in muscle mass, there seems little reason to identify growth hormone as a potential mechanism by which forced repetitions might be effective. Whether forced repetitions could be effective by another means is unknown. It is therefore unclear whether forced repetitions could be beneficial for maximizing hypertrophy.

EFFECT OF PRE-EXHAUSTION TRAINING ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >1 group trained using a pre-exhaustion technique and >1 group did not

Comparator – baseline performance or a non-training control group

Outcome – any measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following study was identified: Fisher (2014).

Findings

The researchers found that there were no differences in lean body mass (measured using the Bod Pod) achieved between the groups as a result of either pre-exhaustion training or similar training without the pre-exhaustion technique.

EFFECT OF REST PAUSE TRAINING ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >1 group trained using a rest pause technique and >1 group did not

Comparator – baseline performance or a non-training control group

Outcome – any measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

The following studies were identified: Oliver (2013), Giessing (2014).

Findings

These studies found differing results, potentially because of quite different study designs and training programs. Oliver et al. (2013) found that both rest pause and conventional training produced similar gains in fat-free mass (DEXA), although rest pause training led to greater strength gains. Giessing et al. (2014) found that the rest pause group displayed an increase in lean body mass (bioelectrical impedance) while the conventional training group did not.

EFFECT OF DROP SETS ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >1 group trained using drop sets and >1 group trained using a similar program but without drop sets

Comparator – baseline performance or a non-training control group

Outcome – any measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

No studies were identified. There is therefore a need for work in this area.

EFFECT OF SUPERSETS ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >1 group trained using supersets and >1 group trained using a similar program but without supersets

Comparator – baseline performance or a non-training control group

Outcome – any measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

No studies were identified. There is therefore a need for work in this area.

EFFECT OF FORCED REPETITIONS ON HYPERTROPHY (TRAINED)

Selection criteria

Population – trained subjects

Intervention – resistance-training, where >1 group trained using forced repetitions and >1 group trained using a similar program but without forced repetitions

Comparator – baseline performance or a non-training control group

Outcome – any measure of muscular hypertrophy (e.g. ultrasound, computed tomography (CT) or magnetic resonance imaging (MRI) scans)

Results

No studies were identified. There is therefore a need for work in this area.

SECTION CONCLUSIONS

For trained individuals, using pre-exhaustion is unlikely to cause larger improvements in muscular size than conventional resistance training. The effects of drop sets, supersets and forced repetitions are unclear. However, the rest pause technique may be beneficial, possibly because it permits greater volume load to be used.


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GENETICS

PURPOSE

This section describes the current state of the research in respect of identifying those genetic polymorphisms that are associated with having (1) a greater amount of muscle mass, and (2) the ability to increase muscular size to a greater extent with resistance training.

BACKGROUND

Introduction

Some individuals respond very well to resistance training and display marked hypertrophy (i.e. responders) while others fail to respond in a meaningful way (i.e. non-responders) even though they are all subject to to the same training program (Hubal et al. 2005; Bamman et al. 2007; Timmons, 2011). This considerable inter-individual variability in hypertrophy has been ascribed to genetic influences, among other things. However, until very recently, the technology was not available to allow researchers to investigate this proposal properly. In addition, some individuals seem naturally to display a higher degree of hypertrophy during development, resulting in more muscle mass in adulthood than others of the same height and gender, even when put in the same environment. The methods for exploring the precise genetic influences on muscle mass have been similarly limited until recently. However, methods for investigating the extent to which heritability influences muscle mass in adulthood have been available for longer, by virtue of twin studies.

Variability in hypertrophy: development

Some reviewers have suggested that genetic factors are responsible for around 50 – 80% of the inter-individual variability in muscular size (Puthucheary et al. 2011), predominantly as a result of analysis of twin studies (e.g. Seeman et al. 1996; Arden and Spector, 1997; and Nguyen et al. 1998). Whether such trials are able to control adequately for differences in the lifestyle of the individuals involved is unknown, however.

Variability in hypertrophy: in resistance training

Since methods have only recently become available for investigating the effect of genetic polymorphisms on the hypertrophic response to resistance training, there has been little research performed to date. Indeed, as recently as the 2006-07 update to The Human Gene Map for Performance and Health-Related Fitness Phenotypes, there was very little research that had been performed to shed any light on the hypertrophic response to resistance training (Bray et al. 2009). Nevertheless, some researchers have since found that a small number of different genetic traits and single nucleotide polymorphisms (SNPs) may be related to a superior increase in muscle mass, which are set out in the table below. Many of the recent trials in the table below have made use of data recorded by the Functional Single Nucleotide Polymorphisms Associated with Human Muscle Size and Strength (FAMuSS), which is the same data set that was used to produce the now deservedly famous investigation into the inter-individual responses to resistance training by Hubal et al. (2005). Recently, a summary of the findings from this data set was produced by the researchers working on the FAMuSS study data (Pescatello et al. 2013). The reviewers reported on the results published in relation to 17 different genes that were specifically tested for their association with muscle strength or size (Pescatello et al. 2013). They concluded that with a few minor exceptions, single variants in genetic polymorphisms appear to explain only minor inter-individual variability in the hypertrophic response to resistance training (see review by Pescatello et al. 2013).

Variability in satellite cell responses

Some of the variability in hypertrophy resulting from resistance training may arise from inter-individual differences in the acute or long-term satellite cell response. Petrella et al. (2008) grouped 66 subjects into extreme responder (17 subjects), modest responder (32 subjects), and non-responder groups (17 subjects) based on their average increases in muscular size (58%, 28% and 0%, respectively) following a 16-week lower-body resistance training program. The satellite cell population pre-training was greater in the extreme responder group than in either of the other two groups. Moreover, the satellite cell number increased significantly from pre- to post-training only in the extreme responder group (by 117%) and not in the other two groups (Bamman et al. 2007; Petrella et al. 2008).

GENETIC INFLUENCES ON HYPERTROPHY

Selection criteria

Population – any subjects

Intervention – long-term resistance training trial

Comparator – baseline and other individuals

Outcome – genetic polymorphisms that were associated with superior of inferior gains in muscular size after training

Results

The following studies were identified: Ivey (2000), Thomis (2004), Riechman (2004), Pescatello (2006), Pistilli (2007), Pistilli (2008), Devaney (2009), Kostek (2009), Harmon (2010), Van Deveire (2012), Li (2014).

Findings

A great many genetic polymorphisms have been identified that are associated with superior ability to increase muscular size in response to resistance training programs. However, many other potential polymorphisms have been assessed and proved to have no relationship with hypertrophic potential.

SECTION CONCLUSIONS

Genetics appear to play an important role in differentiating between individuals who display very marked hypertrophy (responders) and those who do not (non-responders). However, we are currently unable to identify those genes or groups of genes that are associated with responsive or non-responsive tendencies.


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Chris Beardsley performed the literature reviews, wrote the first draft of this page and was the primary author.


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